Getting to large scores in Ars is always doable as a pure thought exercise, but ignores the associated costs to getting to those high numbers. Com 5 has a cost for characteristics (either taking negatives or fewer positives) and either of vis or a virtue cost. Good Teacher has a virtue cost. Teaching has an XP cost, which is really a time cost. Lab specializations for teaching have an impact on other things. I'm going to ignore Apt Student, because IMO it's a virtue for a player, rather than an NPC.
A teaching score of 10 is 275 XP, assuming an average of 10xp per season, that's 28 seasons, or 7 years. And I really do think 10xp per season is a reasonable maximum average xp to earn in a season.
Your average magus isn't going to have good teacher, will probably have a Com 1, and would invest a couple of seasons into a teaching ability to get a 2 or 3. That means an effective teaching SQ for your average magus with his first apprentice is probably Com 1 + 2 or 3 Teaching +1 Specialty +3 Std +6 Single Student for a total of 13 or 14.
So solving for the problem of teaching two major hermetic virtues isn't going to be a common problem. It's an Autmn covenant problem, to paraphrase first world problems.
Most players in active sagas aren't going to invest a lot into teaching an NPC, or even a tertiary PC of another player, unless the story is really compelling. But when you start getting into boosting characteristics, virtues and XP, the story rarely gets compelling.
I have an active magus character, who was a Magister in Artibus, and had invested in teaching at gauntlet with a score of 2. Good Teacher and Com 2. So, he already started with pretty decent teaching SQ, and only had a bit further to go to get to his SQ of 23. Improve his lab, and increasing his teaching ability were the least cost to this character, but it was still a cost. He was geared for being a good teacher, maintaining a role in mundane society AND also being good at Corpus. A lot of other stuff was sacrificed at gauntlet. This particular character is now in the position of being able to teach his apprentice much of what he knows of many arts and abilities in a single season. He struggled to get to the SQ to impart a "free" major virtue and flaw. Most characters won't be so lucky. And we found the effort, as a troupe, to be interesting, and compelling.