It is unknown about Xavi, since he still needs to prove himself somewhere else so that conclusions can be drawn, but Tuchel is definitely better than Ten Hag, he had both successes and failures, but he worked in several top clubs. As for Ten Hag and the players he needed, doesn’t it bother you that with those players he didn’t like he took third place, and with those he bought (having spent 400 million) he took eighth place? I see a pattern here and this cannot be explained by injuries, since other clubs also suffered from injuries but were able to cope with it.
Xavi still needs time to prove his skills as a head coach but in Barcelona, he shown his management well enough. He is not yet a great coach but he won La Liga with them and helped them to go a little bit far in Champions League. He deserves to be respected by Barcelona but they sacked Xavi in surprise because they failed to resolve their internal conflict.
Ten Hag got better support from his club than Xavi but in general assessment, Ten Hag did his job worse than Xavi. Financial statuses of two clubs are different and with better status, Manchester United look to be more calm than Barcelona and they are more ready to give their coach more time to prove ability than Barcelona. I agree that Ten Hag must be frankly responsible with bad performances this season than blaming on many things like player injuries, lack of good players.