Ajax is different from Manchester United, the same way that Manchester United is different from Bayern Leverkusen. He should be given benefit of doubt and not coming to conclusions just yet even when he’s yet to tie charge of the whole team since he was signed as their new head coach. His coordination and the number of matches he’s able to win and performance in those matches will tell how well he can with the club especially in the first five matches when the league begins.
The difference in all teams is very true, there have been times when a coach has left a team and went to another team and did well in their new team than they have in their former team, so it is very possible this can be case with Ten Hag in Leverkusen. He may even be able to replicate his performance in Ajax in Leverkusen. So it will be only ideal to give him time because he may have failed at Manchester United but will do better at Leverkusen. Because everything here in Germany is different from what it is at England and at ajax. He is a good coach and looks very promising in Leverkusen more than Manchester United.