Honestly, I don't think the data is this big smoking gun. The old wisdom (idk if this is still true) is that Tournament and Black Market, two cards known for being swingy, are also both cards that make the better player win more often. The distinction is how swingy they are in the game, and how swingy they are across games.
Here's a simplified scenario. Let's assume that the reason good players win more with Black Market is because they can identify more cards that are important. So say, 20% of Black Market plays win them the game, instead of just 10%. These are just random numbers, don't read into them too much. Then, a better player wins more often because they can identify the extra 10% of wins that weaker players don't. But within the single game, it still looks like "Oh, I got the right Black Market buy and they didn't. That's no fun." Having better odds of pressing the "you win" button doesn't make actually pressing the "you win" button more fun, because there's no art in pressing a "you win" button. It's only fun if you like figuring out how to increase those odds, and it balances out the salt of losing despite playing it right.
So back to Seprix. I never said you didn't like King's Court. In fact, I like King's Court. I don't think it deserves hate, it's a fun card and I like playing with it on the board. I'm also not saying your opinion makes no sense because I can see parts of where you're coming from. The main thing I'm curious about is what makes Peasant special, because as far as I could tell, replacing "Peasant" with "King's Court" required changing very little about the rest of your argument. And as you noted, "Peasant" --> "Page" does a similar thing. It's not just that other cards share situations, it's that these card seem to share all the same critiques.
I wanted to know what piece was missing, that would make the argument only make sense with Peasant, and not with other cards. That, to me, is the interesting part of this. Logical self-consistency is a pipe dream, but in my experience there's usually something that resolves the contradiction (even if it takes a while to figuring out exactly how to say it.)