I don't think it is all about adaptation, but about the quality and balance of the Bayern Munich squad. A lot of people have been saying that this is the best team they ever had, but I never understood why they are saying that. What about the team when Ribery and Robben played on the wings, Lewandwoski in the center, Neuer was in his prime and Lahm also was still playing? Was that team any worse? Definitely not in my opinion and all those players have been pretty reliable if they were healthy. Robben was injured too often, but when he played he was always dangerous. Sané will never replace Robben. Gnabry will never replace Ribery and no defender will ever replace Lahm.
Tuchel overestimates the quality of that team. If they don't add some high quality players, they will have problems again next season.
I'm not going to try to compare with their squad when some of the players you mentioned are still in their squad. However, in my opinion, comparing between the squad before and now, of course, we will always find differences, whether in the way they play or the coach's strategy implemented, because their coach is also not the same as when the players were at Bayren Munich.
The coach's assessment will also differ from their point of view, so it's only natural that their opinion will differ from our opinion of their squad.
Actually, the problem at Bayern Munich is only in the coach and the players themselves.
Both parties should have found a way to get better in consistently working together between players and performance strategies must always be considered.
There are lots of cases of decreased performance and some of them blame the coach and some blame the players.
But I just always hope that Bayern Munich will recover soon like other clubs that have a good future.