I think he's behind De Gea, much as it pains me to say it.
IMO there's De Gea, then another 2 or 3 at a level down (of which Alisson is one), then the rest.
It's debatable whether De Gea could offer what Alisson can to the system that Liverpool play.
No doubt that he's arguably the best shot stopper in the World at the moment
but in the Spanish setup he isn't quite the same.
Keepers for systems. De Gea & Alisson are both currently the best in their respective systems.