Isn't this just us floundering around the obvious answer? Almost ever GT winner started as a young talent able to deliver inconsistent brilliance. They do tours and GTs to build their endurance and recovery abilities and, generally, after 4 or 5 GTs they have climbed the rates and are able to string day after day together and compete for the win. Exceptions to that patter are exactly that - exceptions. Pogacar didn't need that, sure, but Roglic did. Nibali did. Froome did. Contador did (although fewer reps). And so on. Let him ride a few GTs and drop like a stone here and there and earn some results in the 30s and 20s and then let's see. If he beats that, he's beating standard historical precedence.