I mean, "exxxtreme" pretty much describes in one word why this character is so bad.The character is bad but that seems a little extreme. Their is lots and lots of bad characters out their in fiction. Not all of them are at least played by a Oscar winner.
Had they toned down literally ANYTHING - simply made her a normal badguy, dictator, evil queen, whatever, but NOT a leather-clad, edgy dominatrix getting wet by committing actual fucking genocide and cannibalism and revelling in it - none of the criticism would be that harsh.
Like really - why not simply just edgy, but instead so, so, be so extreeeeme?