Dont know why you are saying he is fatigued. Just checked that he played around 60% of available minutes in all competitions this season. Which confirms my eye test - that he often is either subbed at 60-70 minute, or just start at bench.Sarr gets a pass because he is a kid who is running on fumes. If you are a viewer and don't see that then you need glasses.
When Bents gets back and Biss is replaced and maybe Gray gets pushed into MF we will see him release his potential.
Midfield is area where Ange rotates preety well.
He is just inconsistent this season like whole team. Had a spell like month ago when was very good, but right now he is preety average. Major problem is his possession ability. He can't do half turns, and often hides from the ball. Imo he looks best when Maddison is on and drops deep. Otherwise, whoever plays at 6 is exposed because Sarr does not help him during build-up.
He would be great 6 with better ball ability. But as a 8, he might find himself behind Bergvall/Gray/Maddison/Deki/Bentancura preety soon in picking order .