Dortmund hope Sabitzer to fill Bellingham's place nicely. There is a big difference between these two players. While one of them is more of a very young but really skilled midfielder the other one is a much more experienced decent level midfielder. Maybe Sabitzer's talent level isn't high as Bellingham but I believe he is quality enough to keep Dortmund midfield strong. He had a short journey at Manchester United and now he is back at home which is the Bundesliga.
His best times were with Leipzig of course. He couldn't give the expected to Bayern Munich but I don't think it would be the same at Dortmund. Because he can have much more playing time to show a good level of performance.
The departure of Jude Bellingham left an empty spot in the midfield, and they recruited this player to replace Jude well. You're right, maybe Jude's skills are better, but with his experience, he can make up for it. Because after all, experience will greatly affect the player's game. He can better read the situation and what to do in order to be able to take advantage of the situation that occurs on the field.
One thing I would like to see from this club, is the rebirth of talented young players who will enliven the transfer market later.