Man United actually already has a good defender like Leny Yoro but unfortunately the problem that MU experienced last season happened to the player who was injured. I don't know what caused all this but I see Man United more often injured players. This is the reason why Man United performance is a little bad but I also support your opinion if Ten Hag should prioritize new players in the defense line to maintain stability between the attack line and the defense. This is a pressure for the coach, he must continue to fix this problem with the many criticisms that are currently spreading. Ten Hag should have a strategy to cover this weakness by not losing the score in every appearance.
Injury was another factor that affected Manchester United a whole lot last season and of a truth I cannot blame them in that aspect but then they should have plans for unavoidable circumstances as this, now even this season they had another player who suffered injury even before the season began so it would have been even much better if he had played a while for the team but sadly he didn't before he was faced with the injury. I know that things like this do exerts pressure on the coach but then it's always within the coaches discretion to put out strategies and tactics that will help them stay afloat in the midst of all of this.