Erik Ten Hag's performances in the Netherlands propelled him to the Premier League thanks to his Ajax performances, but his team's performances in the Premier League, where the main competition lies, have been quite weak. Now he's moved to a team aiming for success in the Bundesliga, and I don't think he'll be successful there either. His next stop will likely be the Netherlands. He could return to the Netherlands and manage a team. Frankly, his chances of success in the challenging Bundesliga are quite low.
I think it's too early to jump to conclusions. He achieved very good success at Ajax, which already shows that he's a good coach. He came to Manchester United at a difficult time, when the team was already going through a prolonged crisis. He tried to apply the same principles at Manchester United that he used at Ajax, and he brought in many young players. But in the Premier League, it didn’t work because the competition is much tougher and there are a lot of strong teams.
How this will work out for him in the Bundesliga is still unclear, because it’s a new league for him. So it’s not worth making any predictions yet, as there’s a whole season, or maybe even more than one, ahead in the Bundesliga.