If it were simply that, it would have been fine, sure. I didn't especially hate the LOTR crossover either. There was absolutely room for Magic to have, say, one crossover set a year with a fitting fantasy franchise. I'm not saying a crossover is inherently poison that instantly kills a game. What many established players do hate, and what made me understand the game is not for me anymore, is that they broke their promise for these cards to be segregated from regular play, that they started printing more advertisement crossovers than real cards, that these crossovers became less and less appropriate to a fantasy game setting to the point that said setting is completely gone now, and that they started bastardizing even the regular sets (Edge of Eternities is technically not a crossover, but it does not feel like a real Magic set either and clearly only exists to lay down a gameplay framework for the upcoming Star Trek set).
I'm not sure Wizards does understand their market. As you noted, a set doing numbers pre-release has absolutely nothing to do with its quality; it just means there are a lot of Final Fantasy fans interested in collecting cards. But this is not necessarily sustainable for another 30 years, because those Final Fantasy fans are not necessarily going to stick around for Spiderman, and Spiderman fans are not necessarily going to stick around for Spongebob. The Spiderman set was already such a massive flop that they were trying to identify and blame which content creators/streamers were responsible for negatively influencing public opinion, as though that couldn't have happened organically.
WotC is also just about the most incompetent company in the world when it comes to maintaining customer goodwill lately. D&D 5e still, 10 years on, has no real mechanical depth to character building. There's all the identity politics stuff which is needlessly divisive (such as trying to remove "races" and racial bonuses from new D&D rules because it's not PC). They tried to pull that stunt with the OGL where they tried to alter the deal after the fact because the terms weren't to some bean counter's liking. They sent the fucking Pinkertons to raid a guy's house because he got his hands on a prerelease MTG thing through no shenanigans of his own.
At this point, I'm done with WotC. The Pinkerton thing was by far the worst and what made me turn my back forever. Bad rulesets or design designs with which I disagree are one thing, but I refuse to do business with a company that thinks it's acceptable to use force to try to bully people into sticking to their release schedules. They can pound sand forever.