I'm not huge on Archimedes but he's definitely better than Kay and Ector.
Sword in the Stone is middle of the road for me because while it has great scenes and goes to great lengths to get the message that Merlin is sending to Wart across, as you mentioned often times things happen with no build-up because so much time has already been spent on the episodic transformation scenes. Other than the ending (and while I agree that the duel is great) Mim has no build-up. We're shown an evil old lady and immediately she's presented to us as "the evil Merlin". In fact, Mim's first appearance might be the latest in a film the "main antagonist" is actually revealed.
SMDC does sort of spoil the film though because the characters are so massively overrated. Merlin at least makes sense, but Archimedes and Girl Squirrel have performed ridiculous well over the years and it makes me almost despise the latter of those, even though I find the squirrel scene to be very cute and the best of the transformation sequences. I guess I just hate seeing a minor character outlast major ones time and time again.
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Still smilin'
:>