Yeah, the additional point of Finesse does shift it significantly, though I have yet to ever duel in an environment with no aura. Still, botches are relatively rare even in a +3 and wouldn't shift the odds meaningfully in single round duels.
Slightly related, tonight my players decided to do a lot of spontaneous casting in a +8 aura. That didn't work out very well, though only one character entered Twilight and only for a moment.
The aura is irrelevant for most Certamen.
Both sides would add the same value (Aura value) to all relevant numbers, and so it cancels out.
And obviously, Hermetic Magi do not have to worry about extra botch dice from a magic aura.
You might want to think twice about having a certamen against a Merinita while in a faerie Aura, or a diabolist in an infernal aura, obviously.
As Tellus pointed out, note that a magic aura does not add botch dice to magical activities. In my sagas, only a small minority of duels take place in hostile auras or similarly hostile environments (e.g. in the middle of a snowstorm). In any case, I ran a quick check and indeed, Tempestas probability of KOing Venzi does decrease with botch dice, but quickly converges to some 59.1% or so (that's her probability even with one hundred botch dice).
I really like the Venzi vs. Tempestas example in that it shows that:
The botches are the only thing that are relevant. Our covenant is in an area with a shifting magic/faerie aura, so there have been a few times where we have wound up dueling in a faerie (once in dominion!) aura.
I don't want to be too critical since Tempestas does succeed at winning against Venzi more often than not, but she's designed with literally every one of Venzi's relevant stats in mind and for a circumstance where he challenges her to certamen. For a Tremere to win their sigil from their parens, they must issue the challenge. Form selection gives many more options for sucker-punching. If Tempestas were to challenge Venzi, she's close to 100% likely to lose because there's no reason he would suggest either Auram or Aquam during form selection.
I also think your examples of initiative and MMF being very important and not very important aren't practical for most circumstances of certamen. I've fought close to 20 duels with Venzi now and there have been two circumstances where the enemy's offense was so overwhelmingly high that initiative was decisive. Even so, Venzi has still never lost a duel in a single round because the people he duels have not dedicated their lives to beating him at all costs. Similarly, Venzi would not dedicate his life to defeating his Tormenting Master because doing so would make him worse at certamen in general -- this also assumes that a Tremere would have a working knowledge of all their parens' Arts, characteristics, and abilities and that their parens effectively stands still while the filius custom builds themselves up to destroy them. Venzi is a disputant, so he needs to be able to win consistently, over and over, whether he's challenging or being challenged, against a variety of styles. 2:1 conversion from Hoplomachus and doubling the lower art are the keys to this. Going from 10/12 to 20/12 and then to 28/8 is enormous.
I think Bone-Biting is actually the only school where it's worthwhile to fight in the style because the "in the style" rules seem to have been written as follower rules. With many of the "in the style" rules, the main bonuses of the school are cut in half. If Bone-Biter masters were actually getting +15 or +20 to their rolls in exchange for one Light Wound, watch out pre-Schism campaigns, because the Diedne are going to roll everyone.
Tempestas was just meant as an example of the fact that there isn't a "perfect" certamen specialist. Each will have strengths and weaknesses, and in particular will lose in certain circumstances against opponents with far less experience.
Tempestas will almost certainly lose if she challenges Venzi.
However!
Tempestas has a twin, whom her parens found when he found her and gave to a fellow house member for training. This Scalprus is almost identical to Tempestas - but while she is unbridled elemental fury, he is precise, analytical destruction. Mechanically, his stats are identical to those of Tempestas, except that he swaps Aquam and Auram, respectively, for Intellego and Perdo, and increases Finesse by 1 point while decreasing Penetration by 1 point (this "costs" him 4 additional xps, taken e.g. from Charm - leaving him at 840 "relevant" xp, still less than 2/3 of Venzi's 1264). At the Normandy Tribunal, he calmly walks to Venzi and politely challenges him to Intellego or, if refused, to Perdo - accepting any Form Venzi offers save Ignem ("Too chaotic for me!"). Whom would you say is more likely to win the duel?
I agree that the Tremere magical focus is a considerable advantage in many circumstances. I just said that sometimes it isn't. Note that many specialist magi will have one really low Art in the duel (often 0, particularly for the young). Doubling it brings little advantage! Note that this is canonically true for many (most?) Tremere magi too, since according to HoH:TL they tend to specialize in two Forms and two Techniques (a relatively dumb choice, in my opinion, but hey).
Similarly, I never said Initiative is always very important. I think it's important in a large number of circumstances, particularly when vis is involved (an admittedly rare occurrence - but that's when the stakes are really high).
Of course, Venzi is your character, and he acts and thinks as you say. However, I do not think it's that uncommon for a young Tremere to focus his growth during his first two or three decades as a magus (not his entire life!) so as to win his sigil from his parens - whose strengths and weaknesses are probably roughly familiar to him, from long acquaintance. After all, there's considerable honour in being able to do so, and considerable material advantages as well; and the young Tremere is probably only choosing to learn earlier some things that he would have eventually learnt anyways. On the other hand, for the parens "reshaping" his own magical skillset to defend against one of his students has both greater costs, and offers comparatively fewer benefits (having one more underling is less useful than being your own master); I would also say it's seen as less honourable, but that's how I see the house.
Venzi is certainly a very well-rounded duelist. However, in the complex scenario of Hermetic politics, it's usually not magus A vs. magus B. It's the group of magi A1, A2,...An vs. the group of magi B1,B2,...Bn. So, it's not clear to me that a magus who's moderately strong in every circumstance is "better" (and a better asset for his House) than one who specializes for a subset of circumstances, and maneuvers carefully to always be in those. After all armies made of different types of specialized troops regularly outperform homogeneous armies since well before the Iron age!
Let's go for an example. Suppose you are challenged to Certamen. Would you rather choose as a champion Venzi, or an Andabatus magus - even a non-Tremere - who specialized in Finesse and two Forms the challenger is not particularly strong in? For the same total experience, I would choose the Andabatus. That would be double true if the stakes were really high, and both parties were ready to burn several rooks of vis to win the challenge.
I agree that fighting as a follower of a strong school is often a better choice than fighting "in the style" of a variety of schools. But sometimes you are a follower of a really bad school (say, Pumilius), or you are a follower of a school that is not very strong against a particular opponent (Essedarius against a fearless character!). It may then be worthwhile to go for a variety of styles that give you an advantage here or there, even if you don't know Bone-Biting. For example, Andabatus is good for a coupe the grace - you gain the Finesse bonus, but you don't pay the penalty because your opponent is unconscious by that time. Provocator is very good against an Hoplomachus, because you gain essentially a "free" Finesse bonus to your Resistance - which is not vulnerable, unlike the Hoplomachus bonus, to being erased by a botch. And so on.