the work here will be very easy for Ten Hag because he met a good team just as you said but this will also expose many things about him if he is actually a good Manager or not, despite anything I think he didn't do much for Manchester United, he messed up in the club because he doesnt what to listen to may other person except the things he wants to do, yea at a time his former club was lacking players which we know and the ones present as at then was even confused in the football field but I will also say that Ten Hag ran out of ideas then too, now he is here in Leverkusen that has everything he needs definitely there will be expectations from the management of the club, less see what he can offer.
That's the biggest fear he will have isn't it? I mean if he does well, then he will be saying "it was united that was wrong" and get better, but if he fails? Oh boy, that's going to haunt him. Erik Ten Hag needs to do great with Leverkusen and already started to buy up some expensive players like he is still at United, Leverkusen isn't some rich club, and he will ruin the club if these players are bought because of what he suggested, if it was some director or whatever then he is not to be blamed obviously.
I have 90% estimate that he will fail and not be in top four this season, which will prove that he was a bad manager all along. Will that happen? I do not know, I am just making a guess, but I bet that it may actually happen.