Nobody should compare Leverkusen and Manchester United currently cause Leverkusen is in a league where there's not much competition and any good coach would succeed there if they can beat or draw Munich home and away then do well against other teams. It's not similar I'm the EPL where there's Manchester City, Arsenal, Liverpool, Chelsea, Tottenham, Newcastle and even other tough midtable teams to deal with. The Premier league is not for the weak.
I agree with this very much, I have mentioned one of the times that the comparison between Manchester United and Leverkusen is and will never be a comparison that will be equate at any point. These are two different teams in two different leagues with different challenges to face, different types of competitors to handle and different team quality so there is absolutely no way a comparison between this two team will pass to an actual resolve, there will be some imbalance that will make it not a good comparison due to the too many differences.
This is why we shouldn't underestimate Ten Hag. Leverkusen wouldn't expect too much from Ten Hag because they have known his past and hiring him means that they're ready to work with him. On the other hand, Ten Hag will also want to put in the best of his coaching skills into the job, so that Leverkusen wouldn't be disappointed in him.