DS9 and ENT kinda cheapened the Mirror Universe by turning it into a reset button where you can kill off prominent characters or bring back dead ones (Sometimes just to kill them again) with ZERO consequences for the regular timeline.
It's cheap, lzy writing. And DS9 emasculated the MU by killing the Terran Empire
On the plus side Blaylock DID look better with her hair down, and not in that wig.
Defintely agree with you in Blalock's hairstyle...
...and mostly with your other opinion, though I liked the ENT mirror episode(s) very much, as a hommage in an mostly ironic style to the The Original Series. But I wasn't very fond of the DS9 interpretation of the MU as well. Despite the things you already mentioned I always had the feeling that the producers couldn't resist to show that in the end even in the evil MU humans aren't that bad.