Except that the 2 managers that people here wished for instead of Xavi made a fool out of themselves in the last 1-2 years.
I'm going to assume one of them you're referring to is ETH.
United has been a mess since Fergie, and he came in and took over, all the while it being in the best league in the world, by far. I'm not saying he hasn't made mistakes or is perfect, but his situation was shit and completely different than Xavi in Barca.
Xavi walked into a solid team, thriving youth players and 210mil to be spent in 2 windows. He also benefited from RM having their worst La Liga season in a very long time and AM was broke and imploded from Covid FFP restrictions. Ter Stegen had an incredible league season and we were so lucky in defense (I'm laughing out loud literally thinking about how many times we were shit and should of conceded but got lucky).
There is absolutely no reason to think, what so ever, that a proven and experienced coach couldn't easily have won the league given those circumstances, played better football and possibly done better in Europe.
Meanwhile, you put Xavi at United and they'd be even more fucked. He's a coach with no vision, there is no structure or organization to this team. It's been 2 years and you don't watch this team and identify what the style or plan of football is.
Panic crossing to no one doesn't count.
It doesn't end at ETH, there are several other coaches who were not only more experienced but actually have a style in which they coach their teams in. Xavi has been and continues to be a disaster from the moment once the WC ended and the honeymoon phase was over.