All criticism is not qualitatively or contextually similar.
If I tell you, for example, that it isn't raining at the moment, and then five minutes later it starts to rain, that is an objectively true statement. If it hasn't rained for many months and there is no indication that it will do so any time soon, and so I tell you that it is doubtful that it will rain, and then it does rain, I won't look stupid, because that's a qualified and quite reasonable statement given the evidence. But if I tell you that it certainly won't rain in Manchester in the next six months, given all that I know about the weather in that part of the world, then I'd look stupid.
I'm sure that you understand all of this, so I apologize for even mentioning it, but your first few sentences don't appear to recognize any subtlety of opinion at all. Any definitive and final statement is extremely risky and likely ill-advised in football, of course, and I get tired of saying so, myself. But there has to be a difference between a judgment based on two years of evidence, and one based on two months, for example, or else you are literally arguing that there cannot be a point at which anyone could make a judgment without looking stupid if it turned out to be wrong. That would be absurd. It would certainly be a wrong judgment, of course, but the most rational option given the evidence at the time is often wrong.
Two seasons for a player in their late twenties who had performed exceptionally well at another English club and then cost £30m as a result of those performances is hardly the definition of "quick". Circumstances are all important because a young player is clearly different to a player who is supposedly in the prime of their career. And a foreign player who is making their debut in this league at any age is also different to a player who has not only played in the league for several years, but also starred in it. So, it's unfair and unreasonable, in my opinion, to ignore subtle and reasoned opinion in favor of some kind of rigid all-encompassing dogma.
There's no question that a lot of the criticism of Berbatov was unfair and appeared to be a result of an irrational dislike of the player, but those people looked stupid at the time and continue to do so, regardless of what Berbatov does in the future. That is not, and I would argue, cannot be, the same as suggesting that, after two years of generally underwhelming performances, all evidence up to that point suggested that he didn't suit this team, or that his mentality hadn't been right, not least because it's entirely possible that his mentality has now improved and that he finally feels comfortable with the role that he is expected to fulfill.
I completely agree with the point that I believe that you are making, and I realize that I am being slightly pedantic, but we can only make judgments based on the evidence that is available, plus our experiences of previous situations. The difference with Berbatov, as I've already said, is that age and maturity were far less likely to have been a mitigating factor. At his age, it is not unreasonable to either question whether he will ever find the required form, or even to suggest that he didn't deserve the same amount of time as young players do.