I don't think his knee is 100%
It's almost impossible to quantify someone's health but his dunks are down this season and his 3 point shot is nowhere as good which lends me to believe his knee isn't all the way there yet. He was a 40% catch and shoot player his first 3+ years in Cleveland. Lonzo Ball had a similar injury last season and he's nowhere close to getting back on the court.
Of course he's getting like half the minutes off the bench too. Last game he played 17 mins. In Cleveland they just asked him to score but now he's being asked to change his play style but his real game is too damn close to JC's game. Personally I trade JC for draft capital, give the starting role to Beasley, and just let Sexton have those minutes off the bench as the microwave scorer in the Hyland/Poole/Clarkson 6th man role. Just give him a consistent role and build his confidence back up. They can always flip Sexton for picks next season if they want but doing it now would be selling low. This is technically his 5th year in the league so everyone forgets he's only 23, just a year older than Agbaji, and also coming off a fairly significant knee surgery.