Like most reasonable people, I am sure you are basing this on Mikes extensive career playing the position, and Sextons lack of time on ball in Cleveland? He is more than capable of scoring at a higher level than Mike is now, and although he clearly is not proven as a floor general by any means , it seems fairly obvious to me, watching his mental decision making, hearing him barking out there on occasion over the past few seasons, and watching his game film from Cleveland when Garland was out. He has the chops to make it work. Don't see how Mike is really leading this team right now either, the offense is not really running through him for the most part at all, which kills your argument they would start losing adding a more efficient scorer in his place.
All that being said if Sextons oblique is major you won't see him at all for awhile.