Yes. I like it - having Flawless Art as a minor virtue. Are we talking Forms or also Techniques then?
I love Spell Mastery, and consequently I love Flawless Magic, because it makes things so much easier. That being said, I often find difficulty in choosing Mastery for specific spells for my Flawless Magus . All spells are mastered, but low magnitude helper or booster spells which aren't cast during stress don't really need any Masteries. The spells I may have to assist a magus during travel (e.g. ward against rain). The more action-oriented spells need a Mastery, often more the one, and that's where the strength lies.
So what I'm saying is that I like Flawless Magic's component of "quick mastery" more then the "automatic Mastery level 1". If the virtue was split into those two parts I'd only take the first. I've been toying with the idea of changing Flawless Magic, but each component is so much more valuable then a Minor Virtue.
Maybe the "quick mastery" could be limited to value it as Minor, if it didn't use a x2 modifier but rather a x1,5 like Affinities?
Maybe the "automatic Mastery" could require the magus to expend his 2 Exposure Exp to get that level 1 Mastery? And if inventing more than one spell during a season, either Master only one, or divide 5 Mastery exp among them. That is a limitation, perhaps valuing it as Minor.
But for a specialized magus to have the advantages of Flawless Magic in his field, while not taking up his Major Hermetic slot would be nice.
Another idea: What if Flawless wasn't by an Art but rather divided up as Foci and Potent Magic are? That would limit it, and put it in line with the other two Virtues.
Maybe like this:
Minor/Major Flawless Magic (Minor/Major Hermetic) : Within a limited field of magic, with a scope like Minor/Major Focus, you excel at mastering spells. All spells invented are automatically Mastered at level 1, and all exp put into spells are doubled.
In order to not nerf the original Virtue, it shouldn't split the two components. Since even the Major version does not cover all the original Virtue does, the multiplier should not be lowered.
In conclusion, as I think while writing:
The original idea of not changing Flawless Magic but simply adding a Minor version is an easy solution.
Having the minor version covering a limited scope rather than a full Art gives more flexibility but also adds complexity in defining it. Especially if it does not use the Minor/Major Focus definitions.
IMHO a Flawless Technique is more valuable than a Flawless Form, so perhaps the Flawless Art could cover either a Technique or two Forms?