Thing is that playing for us is lots of knowing what's expected of you in terms of organisation, when to press, where to cover, understanding every single job around you too so you instinctively know who is doing what (and occasionally being able to do that job if called upon) so you can play the press and counter instantly.
It's knowing that if you don't do that job properly all the time the system breaks down and we get into trouble. Even very good players with years under their belts take time to get it (Ox, Keita, Fabinoho recently but the entire team for 2+ seasons when Klopp arrived first).
On top of that you have to have a skill level or drive or other quality that sets you apart from other footballers for it to be you in the starting 11 and not Bobby, Origi, Minamino, etc.
We know the kid can score. Can he do everything else that's needed at a high enough level for 70-90 mins and still be scoring? We don't know. People hold this against Wilson, I hold it against Origi, who knows for Brewster?