For me the problem is not squad depth but the manager is not able to make the most of the quality of the players he has. Arsenal, Chelsea and Liverpool also don't have much better squad depth but their performance this season has been much better.
Manchester United have fulfilled all Ten Hak's wishes in recruiting new players but he has not been able to deliver good results for the team.
Faulting the manager is crazyy, yes he is also taking responsibility but do you want to blame him for the individual error caused by Casemiro during the game against Liverpool? Do you want to blame Erik Ten Hag for the players not converting the chances they had against Crystal Palace? What about the individual error caused by Harry Maguire during the draw against Brighton? How about the individual error again from Harry Maguire and Christen Eriksen against Twente? Y'all Manchester United are bloody inpatient punks who wants to see quick change that won't bloody last. I'm disappointed, and even if they want to sack EtH, y'all want to settle for mediocre managers.

If the player you are referring to made a mistake in just one or two matches, then it might not be a problem. But after all, Erik ten Hag always plays players who have problems like that and even, Erik ten Hag dumped De Gea at that time, even though in that season De Gea was the best goalkeeper in the Premier League. Also, if you think Erik ten Hag is a great coach, then Erik ten Hag should be able to solve the problems that occurred at Manchester United. After all, as has been said, Manchester United has followed all of Erik ten Hag's wishes in selling players and buying players but the results are still bad.
Those three seasons are not a good time for a coach to build a team with all the wishes followed, but the coach still makes mistakes in making the right strategy and tactics for the team. Thus, it is natural that Manchester United fans want Erik ten Hag to be fired. Manchester United is a rich team with good finances, but its performance is very bad. Look, how other top teams have good finances too, many of the other top teams are successful and not like Manchester United who are only struggling in the middle of the standings.