Why does a dent to a tweeter not affect sound quality?

dented ’dust covers’ on mid size or large concave cones can be inconsequential, they are still moving air, not perfectly, but a small fraction of what the coil/cone is still doing properly. The dust cap is covering the wire coil and the magnetic gap it moves in/out of.

dented is one thing, maybe the dog bumped his nose into it. Cracked, allowing dust, dry or moist air is another, avoid that. dust caps can be replaced.

dented tweeter, that’s bad, stay away.

OP said dented TWEETER.

not a dust cap, the material of the tweeter's driving face, designed specifically, by computers, by sound analysis in industry designed chambers, to  push air at accurate infinitesimal frequencies, the surface creating the accurate specifically designed polar distribution pattern.

Ye that buy fuses, horribly expensive tweaks, and have the nerve to say, my ears aren/t aged like science says, I can hear highs, I can tell the difference between this and that, 

OMG, stay away from dented tweeters!