Idk if Sexton can ever be viewed as good defender. He doesn't have high level instincts in that end required to be a plus defender as a small guard.I think he is pretty close to the point where he should be viewed as a good defender. He puts in effort on that end of the court and has dialed back the intensity level a bit that constantly got him out of position. When I played ball my favorite guys to play defense with were the ones that didn't really gamble and focused on just guarding their guy. The worst was when you played with guys that constantly gambled and forced other teammates to rotate and cover their mistake which then led to an open man.
He's does a good job of not being free lunch when he is there. But sometimes he doesn't always get there. And sometimes he does everything perfectly fine but the other guy just shoots over him