According to the Doctor In (Faculty) virtue the character has spent 10 years in training and gets an additional 300 XP. I read this as gets 300 XP instead of normal yearly XP. A different reading would be to take the characters age defined XP total and add 300 to it (450 XP I think).
How does this virtue work for Hermetic Magi. A virtue of: add ten years to age and add the same 300 XP you would get from taking 10 years after gauntlet isn't all that useful. By contrast, gain an extra 300 starting XP is pretty good.
We have in current ArMDE text under Doctor in (Faculty), that:
The character has spent ten years at a university and receives an additional 300 experience points, which must be spent on Latin and Academic Abilities. He also begins the game with an Academic Reputation of 3.
That makes an Hermetic Magus cum Doctore at the verrry least 30 years old: 5 early childhood, then 15 Hermetic Apprenticeship and finally 10 University studies. So he would soon desire a Longevity Ritual, and be out of touch with the Order and any Hermetic lab for a decade. Getting 300 extra xp in Latin and Academic Abilities as a recompense for that looks quite OK to me.
Anyway, taking such a start for a beginning character will certainly be adjudicated by the troupe in detail: don't espect that corner case to be crammed into ArMDE still.
It is quite possible to pursue an hermetic apprenticeship in parallell with academic studies.
It might be rare, but nothing in the rules says or indicates it can't be done.
The xp from any of the "academic degree" virtues, like Baccalaureu, Magister in Artibus, Doctor in [Faculty], etc. are in addition to whatever xp they get from elsewhere. This is no different than xp from virtues like Educated, Warrior, and the like.
It's also not particularly useful. By RAW a Magus post gauntlet gets 30xp/year. So unless Doctor In also lets you get 15Xp/Year for age, or can be taken at the same time as a hermetic apprenticeship, it has little value.
Personally, I think it should be able to be taken with an apprenticeship. I'm writing something for self publication and want to make sure I get the XP total right.
In that case you best avoid weird corner cases of pre-game development and switch to standard in-game development of the character soon.
Metacreator is a great help for this, and MoH provides good examples.
So how did the character get the degree of a Doctor in (Faculty)? How long did it take? Did he do some creative cheating befitting a magus? Did he still operate as a magus during his studies? How did that affect the relations to his colleagues at university?
Then you see best what the magus' development was in that period.
By Hermetic tradition, a master needs to give one season per year to his apprentice. The three remaining seasons are spent serving the master. So a generous mage could let an apprentice attend in parallel University teaching, accruing the 300 XP of a Doctor, taking about two seasons a year - it is probably in Arts & Academe that I read that university teaching were taking two seasons a year, but serf's parma. I might be mixing up the duty of a professor vs the cursus of the students.
Otherwise, I agree that without assuming that the education was done in parallel, it is not a Major virtue for a mage.
Sure: mechanically taking Doctor simply adds 300xp to the xp total a character would otherwise have, without adding to a character's age. Of course, there are constraints on how those xp can be spent (and on the character's final age - magi in my sagas are often 2-3 years younger than 27-Int). As you noted, it's not a big deal for a magus: those 300xp are in stuff that does not significantly improve a young magus' supernatural puissance at the start of the game, and they are in any case easily acquired on the cheap once gameplay begins, as a covenant can hire a mundane scholar as a one-on-one mentor for just a little silver.
It's up to you to explain how an e.g. 24-year old magus might have managed to complete both his apprenticeship and his doctorate - particularly one without the Gentle Gift! A generous master, one who lost (or decided to win) a wager, a Blatant-Gifted one who wants to influence the academic community through his Gentle-Gifted mentee ... or maybe some strange supernatural effect whereby the magical apprenticeship took place in a university student's dreams.
That depends on the saga.
Hiring intelligent people from outside for some time also means, that these observe and later talk. Good scholars also typically have alternative job offers from Church, universities, law courts and/or in the retinue of nobles - positions with better reputation and long time perspectives. Recruiting instead among failed students or defrocked priests has other risks: the number of venturers, scalpers and other opportunists among them might be high - and maltreating one might scare off all scholars for a long time.
The reputation among mundanes of a covenant trying to hire decent scholars may be decisive in any case.
I like how you think! Now I have an idea forming for a Tytalus apprentice using a (demonic?) supernatural tutor and and a Persona to get both by age 25 or so. It's a neat idea, not at all strong, and probably leads to a bad end very fast unless there is some way to manage a non-demonic tutor. A daimon works lore wise but it's a little far fetched to have an apprentice make such a deal with a daimon but perhaps the Muse of rhetoric or comedy?
That's would work although it might depend on whether your saga would allow it without being initiated into the Titanoi. Doctor in (Faculty) is already a weak major virtue but 3 points on that plus 3 more on MMF in Spirits, 1 in Hermetic Theurgy, and 1 in Persona feels fairly bad mechanically even if I like the roleplay side of the idea.
Edit to add - the MMF in spirits might or might not be weak by itself. It is weak in my opinion because I generally prefer mMF + some over virtue. Plus it doesn't really match my thoughts on a magus who really wanted to be a med student very well!
There is nothing weak about Doctor in (Faculty). 300 extra xp is a lot, even if much of it must be spent on specific abilities - but many of them are abilities an Hermetic Magus want anyway.
I really like the extra XP and the idea of magi who aren't completely focused on magical power. But it is also, I suspect, highly saga dependent. Will having a mage who is skilled in medicine, AL, or so on actually come up in play or will that role always be taken by a learned grog?
Being skilled in Artes Liberales will be useful for magi quite often.
Any time you need to cast a horoscope, or cast a ritual spell, or use ceremonial casting.
Plus, of course, more mundane uses.
Latin is also of obvious use to magi.
Medicine/Theology/Law not so often - but that is saga dependent.
That's the fundamental issue. Doctor in (Faculty) is a great - almost necessary - Virtue for a Companion to be played as a senior academic, particularly when "boosted" with other relevant Virtues. It's not just the xp that matter, the reputation is quite a big deal too.
Doctor in (Faculty) is just a decent Virtue for a magus who wants to portray a mundane scholar who is also a magus (in part, because of the Academic Reputation). But it's certainly not that strong a Virtue, because intrinsically "dual role" magi (magus-academic, magus-knight, magus-artist, magus-holyman etc.) are not that effective as the synergies between the two roles tend to be weakish. It's generally much more rewarding to take a magus as ... a magus, and a mundane doing mundane stuff as a companion.
This is certainly true at character creation, when xp are relatively few and best focused on the magus' magical puissance (Arts, a little Concentration, Finesse, some Magic Theory, a Mastery or two etc.); so that Strong Parens + Gild Trained is probably at least as effective as Doctor in (Faculty) despite providing only 180xp vs. 300, because it's 180xp in stuff that really makes a big difference. In this sense note that Latin 4 + Artes Liberales 1 is very useful to a starting magus, so those first 55xp of Doctor are about as good as 55xp in the Arts, Finesse etc provided by Strong Parens. But the remaining 245? Still somewhat useful (Artes Liberales 5 and Philosphiae 5 - remember the age cap - is good for ceremonial casting, for example) but not nearly as useful.
It's also true as gameplay begins, because really, a grog teacher who can generate high Advancement Totals in mundane stuff for his mentee magi is both very easy to make as a starting character and very easy to justify - almost stereotypical. In fact, the impoverished Baccalaureus of great intellect and learning but little means was a staple of medieval tales; and a covenant can offer a lot that the Church, Universities, Law Courts and/or the retinue of nobles will not offer, or at least will not offer to many. Suddenly 300xp appear a lot less if they are in abilities in which a magus can routinely get 20+xp/season, as opposed to e.g. Spell Masteries or starting Arts (that just push you to the level of "big gun" spells right from the start).
If you plan to cast magic Ceremonially, or cast Rituals, then AL and Philosophiae come up very often.
If you're a Verditius, your Philosophiae can help with enchanting once you've initiated Elder Runes.
I'm well aware of what you are saying with regards to what is considered the normal Ars Magica world and rules as written. I lean towards a very different style of play which is why I emphasized the saga dependence.
In my dream sage (grogs are redshirts, specialists have to be companions or occasional limited time affairs after an adventure, covenants are smaller, and The Gift and magic in general is a much bigger social problem) it might be more important for a magus to know non-arcane skills or have a reputation in the mundane world. As written it's always better to have a specialist grog and the question is much closer to how useful is an early higher total in AL and philosophiae?
Grogs can't have Major virtues or flaws, so for specialist academics you would have to make them companions instead.
Just a small aside, which probably doesn't change much if anything for you.
Of course if you plan to cast rituals you might want Mercurian Magic which you can't get if you are a Titanoi with a MMF in spirits. That also removes Verditius. In this case it's more the interesting, to me, story of a Tytalus apprentice maintaining a sort of double life by using a supernatural tutor that makes AL and Philosophiae less useful.
Depends on how specialized you want. Three minor virtues plus the ability to bootstrap in a covenant that already employed one good teacher to teach the others how to teach can get pretty decent even if not as good as a companion could get.