I'm surprised bishop/silver doesn't show up for P2, and surprised militia/silver doesn't show up for P1. My nonsense theory for hermit-silver: these game tend towards fast three piles, which has more ties than average, which favors P2.
I'm really surprised that there are mirror openings where P1 has a 70% winrate... that means there are kingdoms where P1 is heavily favored.
I think you are wrong with you last implication.
What it says, is, that there are card combinations, that are bad to mirror as P2. It does not say, whether there can be other cards to minimalize this effect (because now we're looking at mirrors). For example, if your P1 opponent opens Swindler/Silver you could try something else like Remake/Silver, so that the advantage of P1 goes down by a few percentages. Maybe, if my opponent opens with an attack card, I am more likely to invest into defense like a moat or something, and maybe this can be better than mirroring what P1 does.
Btw. I am surprised not to see any Witch-openings in the list of P1 advantages.
The idea that you should do something different as player 2 because you're player 2 is almost always just wrong. There's usually a best thing to do, and you should just do that. And when this isn't the case, you're usually adapting because some strategy is a little better against what they did, and it was close to start. You're really almost never never switching just because you're p2.
Yes. The thing to keep in mind is that there are common events that can take place on T1-T4 that are comparable in effect to P1 advantage. Examples: bad opening split, bad money distribution on T3/T4, or a key opening buy missing a shuffle. With Tournament/Ambassador, some additional specific unluck examples that can occur are Ambassador hitting 4 coppers without a good $2 on the board, or various mishaps in the process of gaining a Province and connecting it with Tournament. While any of these individually may be of greater or smaller impact than P1 advantage, the point is that P1 advantage can easily be overturned by events within the game.
I don't think that's true.
1 - bad opening split:
Talking about a board with Ambassador/Tournament and a situation where you could mirror P1 means, that you both have a 3/4 opening. There is no luck involved.
2 - bad money distribution on T3/T4:
I claim, that's no problem. Best thing for your Ambassador turn would be Tournament + Ambassador + 2 Estates on T3. Returning 2 Estates would still mean only $3. Without the Tournament, if you give back 2 cards with Ambassador, you cannot have more than $2.
The worst thing would be Amb + 4 Coppers. If you cannot buy something useful at that price point, you're "thinning" more than the other player who bought maybe a 3-cost.
Best turn with Tournament would be Tournament + 5 Coppers giving you $6 (or maybe $5 is just as well depending on the board).
It's tough to say, but I think, only the last thing really matters...unlesss...your opening buys miss the shuffle.
3- key opening buy miss the shuffle:
Given that we mirror each other, the worst thing to happen would be to miss the shuffle for both of your cards. Chances are 2/12 * 1/11 = 2/132 = 1,5%. With a cantrip like Tournament, the second worst would be for Ambassador to be the last card and thus miss the shuffle. Chances are 1/12 = 8,3%. So basically, my opponent gets bad luck on ~10% of all those games. Unfortunately, my own luck will be bad also on 10% of all games, thus remaining a ~9% chance for my opponent to stumble and me not to.
So, yes, chances are comparable, but still my disadvantage of ~10% is bigger than my chances to cover up due to luck (9%).