I've noticed some objection some people have the magical focuses, and I can see how difficult they can be to manage as an SG.
So, I've been thinking up some alternatives, if those were to be replaced in a future saga. This is a thinking out loud post. I haven't actually done any thought experiments on these to determine where the problems with these virtues are, although I see some potential problems. Superlative Technique may be as awesome of a Virtue as Deficient Technique is heinous. It might be that someone who takes Superlative X needs to take Deficient for something else...I dunno.
Superlative Technique Major, Hermetic
All totals, including Lab and Casting totals involving a particular technique are increased by 50%. Study totals are not increased. Calculate the totals, based on the actual value of the score, then increase by 50%. Bonuses from Superlative Form do not stack.
Superlative Form Minor, Hermetic
All totals, including Lab and Casting totals involving a particular form are increased by 50%. Study totals are not increased. Calculate the totals based on the actual value of the score, then increase by 50%. Bonuses from Superlative Technique do not stack.
 Who has played with Deficient Creo? That is a brutal one, that almost necessitates hiring a Longevity Ritual specialist.
Hiring a longevity specialist is quite normal, so I do not think this to be a specially crippling flaw. Not more than deficient rego for example.
What you are getting here is an improved version opf a focus, sicne it aplies to everything with a full technique (10 full Te+Fo combos), not the much smaller focus advantage. I am not sure I like this but am willing to listen
Highly overpowered, in my opinion, particularly the Form one. Compare it to an Affinity, which boosts only the Form (not the whole total) and by a lesser amount (and, roughly speaking, having a low score plus a high bonus is better than having a high score, because the low score is easier to raise -- even though the high score makes you a better teacher).
Much more powerful than a focus, for two main reasons:
A Major Focus only applies to the equivalent (slightly less) of a Form, while a Minor Focus applies to the equivalent of a TeFo (one fifth of a Form). These would apply to a whole Technique (twice a Form) or a whole Form. So between twice and five time as extensive.
The bonus applies to the complete Lab or Casting Total. That includes Int, Magic Theory, Aura, virtues that add a flat bonus, other abilities that could be added as well (Verditius Magic and Craft ability to item enchantment, Artes Liberales and Philosophiae to ritual magic, etc.)
In short, even the Superlative Form is more powerful than a Major Focus.
Remember, a Puissant Art only add a flat +3, for a minor virtue. Even for an below-average starting magus (starting Art score of 10 in his specialty) with one of these, so this would provide a +5 bonus already, counting only that Art.
Want something more balanced? Try a Major version of Puissant Art, which provides, let's say, a +10 bonus. It will be less powerful than either of these. Maybe Focus should give a flat bonus instead, if you want to cut it down to size.
You're also missing what I think the good part about focus is. A focus gives a character a much stronger theme than some art specific virtue. A focus in bronze or fear or ducks is a heck of a lot more interesting than a bonus to terram,animal or mentem.
One reason why focus works for those of us that like it, is that it is a big enough bonus that a character is very often pushed towards using it. If you have a focus in human bone it will be easier to build a bridge out of skeletons than out of wood. If the bonus is smaller then this may no longer be the case.
I threw this out as an extreme. I'm not planning on doing this, I just thought I'd generate some discussion amongst the people who don't like magical foci. I agree that 50% is too strong. I had to start somewhere, and doing it in the same proportion as Deficient Te/Fo seemed to be a good place to start.
I think the gold standard for a Minor Virtue is +3 to casting, lab, or study total, applied under limited circumstances (e.g. Method Caster). Yes, this does mean that Puissant Art is worth about two Minor Virtues (Puissant Caster with Art and Puissant Labwork with Art); but you knew that i was powerful, right? All the munchkins get it (well, if they can't get Affinity).
The problem is that adding +3 is just not enough of a boost to be a "focus"; more like a quirk. So I suggest increasing the bonus to +6 for a Minor Magical Focus. This is still not terribly enough, even though it's too powerful for a Minor Virtue, so I suggest:
A Minor Magical Focus provides a +6 for TeFo (well, almost).
It also provides a -3 for all totals outside this focus. This both balances the virtue somewhat, and increases the focus of the character's magic.
A Major Magical Focus provides "two" minor ones, for a +12 bonus and -6 malus, and increases the field of applicability to Fo (sort-of).
I think this highlights an important, and often disregarded (sometimes even by the canon products!) point of game balance: if a Virtue provides a bonus identical to the penalty imposed by a Flaw in the same circumstances, the two are not balanced, contrary to what one may think. Instead the Virtue is worth more than the Flaw.
That's because a character with the Virtue will actively try to capitalize on it, taking actions that will maximize its applicability; at the same time a character with the Flaw will actively try to minimize how often it comes into play. For example, we expect that a magus with an Ignem Affinity will specialize in Ignem magics, whereas one with a Deficiency in Ignem will spend very little time learning/creating Ignem magics. It's not munchkinism: most of the time it makes a lot of sense in character, since it's natural for someone to play up one's strengths.