He'd be better for the Lakers than Westbrick, tbh. As a non-Lakers fan I'd be pretty fearful of that lineup. Simmons really wouldn't have to do much more than be an elite defender and get the ball in AD and Lebron's hands.
Westbrick just seems like he'll be in the way on offense and not much he can add defensively. I actually hope the Lakers don't warm up to such an idea.