This is directed mainly at chwhite, but also at everyone.
First off, on the stats: You talk about having small sample size effects. You do realize that the 'I have only skipped it in 5 games' isn't the only small sample size issue here, right? Like, those 10 players have what, 50k games? Or something? That's actually not a huge sample to start with, but then you switch it over to adding in they have to have yea-so-many with the card in question... it becomes sketchy. But then the bigger thing is that I have, personally, over 10.5 thousand Iso games. Those come against so many different opponents on so many different boards at some many different points in my skill level, from first and from second position, and they all just get lumped together. So but the biggest thing here is opposition. I have tons and tons of games against level 20- players. And I have tons and tons of games against 40+ players. And almost certainly, my mix of cards that I get in against these different opponents is pretty different. The issue here is that absolutely every one of these stats is based off of winrate. So first of all, my winrate is way more dependant on the strength of my opposition than most anything else around, including the specific cards present. So I have pretty bad effects with Hinterlands cards. Why? I'll tell you - mostly, it's because these are the newest cards, and it's most recently that I've been playing thousands of games against the other strongest of the strong. So even if I may be actually playing better now, just looking at winrate, it looks like I'm playing worse. Because I win less. But that's not on the cards I get, or the skill I'm showing, but mostly 'cause my opponents are better now. It's the same reason my level keeps going up as my winrate keeps going down. Now, what does that mean? Well it means there's pretty big incongruities and biases in your data, which is going to largely invalidate it. And yes, over large sample size, this should even out, BUT... I think we're well, well off from that. On top of the effect with(out) numbers being totally skewed if you don't account for how often the things are bought, and also that your opponents very often buy the same cards you do when you buy them, which skews the numbers again.
Now tournament. Tournament, I have long held, is a card that takes a lot of skill to play, but which also is one of the swingier cards in the game. It's not the swingiest (which I think is swindler, even above treasure map), but it's up there. Now why do I hate tournament? Do my tournaments get blocked and/or do my opponent's? This is the same issue, almost exactly that mountebank has. Mountebank itself is pretty swingy, and this subsumes most of its luck just right there, which isn't even close to the biggest thing about it. Ok. Now, I agree with you, you can really build a deck around getting your tournaments to go off, and basically this means an engine. But before we even get to the main issues there, let's talk about when there's no viable engine. So here, you very often just skip the tourney if there's a good BM option out there. But your opponent can get lucky and hit (a la treasure map) and while you're not lost, it puts you in a very difficult situation. But okay, let's say you're building that awesome engine. Now your opponent can still spike an early 8 for a province, or play a more BMish thing, hit early, or just block your tournaments which really slow your build-up, and again, you're backfooted, even though you're playing right. But okay, finally, and this is the really big thing. I know that I need to play an engine, you know that engine is the way to go, we both do it, invariably one of us gets to the key prize first and... unlike with most engines, that's basically just it, because I have no recourse to make this advantage back up later. And unlike most cases where I have no recourse, the game is going to go on for a good while longer while I get pummeled, because it's not that you've beaten me to the mega-turn. And there's LOTS of luck (lots of P1 too, but lots and lots of luck) as to who hits first. You probably don't want to wait to get the province until you can reliably draw your whole deck to buy province, because that'll be too late. So maybe you're drawing half your deck, or probably a little more. Okay, that means there's like a 30% chance or something that you hit in any given turn (you have to draw the tourney with the province before you play the tourney, and you have to worry about other tourneys getting blocked... eh, it's going to be higher than this sometimes, but probably not more than 60% or so, at least very early on), and the same for your opponent. Okay... that's pretty swingy as to who gets it first. So I mean, this is way better than if you've built it poorly, and you have, like a 10% chance on any given shuffle, let along turn. But that's still a lot of luck. And it's just so very frustrating to get your door punded in by followers, a curser AND discarder, or to get your usually-a-peddler turned into nothing. So that's why it's among the handful of my least favourite cards. And I don't know about the other top players in general, though I do know Marin has often told me he absolutely hates it.