Harry Potter
Yeah, he's a great teacher. But he's got plenty of examples. And he's been through more school than Hagrid. Harry is arguably one of the best DADA teachers during his time there. And I think he really benefits from NOT having to teach Draco Malfoy.
Firenze:
I disagree. He's only marginally better than Trelawney on the fact that he actually knows stuff. Divinations is such a silly subject anyway so it's hard to tell. But does anyone really learn anything from him? Not to mention a lot of Trelawney's predictions actually come true.
Lupin
He may actually have experience. He may have done some private tutoring (thus explaining his tattered briefcase saying Professor R.J. Lupin".
Barty Crouch Jr:
He also achieved OWLS in every subject. Something even Hermione didn't do. So I'd say he's in general very smart.
Amycus Carrow:
Disagree. Sure, he teaches Crabbe and Goyle something. But they did manage to get through most of their classes before then. And it's not like Crabbe can actually CONTROL his fiendfyre. If he could, then I'd be impressed.
Wilhelmina Grubby-Plank:
She's a substitute. She probably has lots of experience, given that the previous Care for Magical Creatures Professor was injured enough to retire.
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See You In Another Life, Brother.