He's what, 34? It's painfully clear that he has to learn on the job. You're having Jim Rutherford and Ken Holland pivoting their management after learning on the job in their 60s ffs.
His most obvious drawback was he completely disregarded the value of meat and potato players and how different lines at different TOI, deployments, special teams etc need to be able to play differently. The fact that his answer on D was Ceci and Barrie, his 4th line has always been a mishmash of leftover AHL/dumpster dive players and he doesn't have a single proper PKing center says it all. Also thinking backup goalie was a position he could wing after watching Chicago win the cup in his 20s.
That said, some of the things he has done were good (Muzzin was a near perfect get) and he's trending better with getting Clifford and Campbell. But he should have gone for DeMelo/Vatanen (maybe both) while moving on from Ceci and Barrie if the right trade was there for him. And if his gambit with sending Lehner to Vegas gets the Leafs a playoff spot over the Canes that will be one of the coolest subtle GM moves in a while.