A few thoughts from my Bayernfan-point-of-view:
Sabitzer had an abysmal first year. He played very poorly and it clearly showed that he was lacking confidence. In the end he didn't play much last year.
Then, in the summer he had a good pre-season. Gravenberch had a good pre-season as well, yet it was Sabitzer who occupied the vaccant midfield slot in the abscence of the injured Goretzka at the start of the season.
Bayern as a team did well and he also was playing very solid. Many Bayernfans liked that he provided a nice balance in the central midfield with Kimmich. After a few bad team-results the "hype" faded a bit, but he still was doing solid.
The first "big game" of the season was at home against Barcelona. Bayern had no control of the game and Sabitzer was very poor. He was subbed off for Goretzka at half-time, which was one of the factors which changed the momentum of the game.
After that there was a further bit drop of form and Nagelsmann tried to phase in the (injury-prone) Goretzka. Sabi started the next big game: Away in Dortmund. He got an early yellow card and showed another poor performance and again was subbed off at half-time.
Since then he hasn't started one game (excl. the last CL-group game) and is used as a sub- however other players have overtaken him now in the picking order, even Gravenberch.
If you ask me for his strengths and i weaknesses i would honestly struggle. He can be a solid player, runs a lot, good fit if your team is pressing, he seems down to earth and doesn't throw a fit when he isn't playing. We havent seen any of his goal-scoring abilities (especially long shots) which he was supossed to have at Leipzig.
Maybe he can find this quaility back with more confidence which seems to be an issue. I didn't like his passing, it seemed quite limited. Overall not many striking strenghts.
I really don't want to spoil the transfer for you. Keep in mind that it is a very hard to play in the Bayernmidfield since we are only playing with 2 central midfielders and have a very attacking style. Bayernfans are also very critical with their players, especially their midfielders (you should read the comments on Goretzka lol).
The biggest take-away from my post should be that your club really has to make sure Sabitzer won't lack confidence.
