That's an odd argument. Playing with, say, a high defensive line isn't an inherently wrong tactic but it's sure as hell wrong your defenders all have the pace of Maguire.
If you don't have the right player for a certain tactic, then you play a different tactic. "If he had Kane it would be the right tactic" - that's not how it works. He does not have Kane. He has Weghorst. The player he wanted to bring to the club, a player we went to great lengths to extract from Besiktas. It is very much his player, despite your assertions to the contrary and his failing to make him work is exactly that, his failing.
We use wan Bissaka when we want to hold back an opposition left winger, we use Dalot when we want more attacking on the right flank. We use Fred when we want a 3 lung player in the middle of the park. It’s not all the time so he doesn’t get used all the time but it’s obvious what it’s for. We use Shaw because he is left footed and can play the ball whilst Martinez is injured.
Sabitzer seems to score a goal from CAM by making runs in to the box. Sancho plays like Mata.
We bring Maguire on when we needing some heading ability at the back.
Nearly every player is utelise differently offering different things.
Ten Hag clearly had a tactic against west Ham where Weghorst was part of his tactic - I don’t know what’s so odd about it.
When City want a goal scorer out wide do they play De Bruyne, Foden or Mahrez? They play Mahrez because that’s the tactic and Mahrez fits that role the best for them.
Ten Hag had a January transfer window where all he was allowed was Loan signings - if that leads you to believe that he was dying to sign Weghorst even if he had money to spend on him then so be it.
Sabitzer and Weghorst are not United quality and was asked to be bought because that’s literally all he could afford in January.
More examples of individual tactics - Martial to play in Rashford from deep. Bruno as the teams mains creators. Antony seems like he carries the ball/progresses with it forward even if he doesn’t do anything with it.
Every player plays football differently and a combination of them makes a tactic.
If Ten Hag believed defensively he needed a physical heading type defender then who would he choose? Maguire. He has done that this year even after dropping him - bringing him back for a specific opposition led tactic.