That's exactly what I'm unsure of. People don't like to hear it, but team management in football at this level can be a zero-sum game in itself, especially when you already got a strong side and a winner one at that.
So, while it's easy to identify an obvious problem (again not all top clubs employ that player), it's less obvious to know how much you will lose by replacing one of the players who made the team strong in the first place. Like I said, we hope it's a net positive in the end, but I daresay we don't really know that at this time.
This is a time we need to trust the club and Tuchel, since he seems to think it will be a net positive.