A keeper like Alisson is better overall. His positioning within goal to prevent shots, David, is very good. As it relates to sweeping behind his defense it isn't as good, but we all know he doesn't go outside his box much in relation to clearing the ball as a last man preventing a potential shot.
And handling, by way of catching and palming the ball away and limiting rebounds, David is very good.
You're very critical of de Gea and I wouldn't believe that you wouldn't have been very critical of David for example when he came out aggressively from his line against Norwich in the first half to block Pukki's shot near the top of the box.