The key usage is for condescension. "You're not on my level" or "we can't have a proper conversation as peers" so I don't think dumbfuck captures it because we're all dumbfucks. Idiot and moron are bland but lack impact.

Neanderthal and subhuman I hate. If you're on message and on the left you should be averse to dehumanising language in principle.

So I'm for "lil bro"ing, I'm for riffing on teacher/student, I'm for grounding people because you're fucking their mom, I'm for anything which says "you're opinion is invalid".

So remedial is ok, but ultimately targets people who are likely to be listening so b the collateral damage is too high. So if you can't think of anything more creative from the above I would advocate for the monosyllabic "dunce" which is anachronistic so it doesn't have the same collateral damage even if it means a similar thing.