Sexton has been playing better and you have to give him credit for that. I certainly can't say he has been the reason for the losses (everybody on the team has weaknesses which have become more apparent). I personally still find his style of play incredibly annoying though. He does many things which drive me mental when I am playing basketball and are to the detriment of the team.
- Holding the ball too long and missing mismatches early. By the time he notices its too late and the offensive movement completely stops.
- Not advancing the ball with a pass early enough and coming back for the ball. This one particularly drives me crazy when I play. If somebody is already bringing the ball up the middle (and no pressure) don't come back towards the ball clapping your hands. Run the lane. Then if you are the one with the ball, if somebody is open on the wing for a drive, pass it early. Don't slow the game down by dribbling it up.
- High intensity, low intelligence defence. Clapping your hands, getting right up on somebody who is not even in the play yet. Then getting caught on every single screen because you have no court awareness.
In general I think he is a player that doesn't yet understand that you don't have to be the one directly doing something. Eg, if somebody has a mismatch in the paint and you are at the top, don't force a straight pass. Flip it to the wing and let them pass it in. You see somebody open early on the break, give it up and then run. You don't have to drive it right into the rim for a dump off. If he doesn't develop the understanding for that, he should be used as a 6th man.
Just tell him directly.