She can combo every character in the game off of basically any of her moves, she has a combo that can kill almost every character in the game from 0% even with good DI (directional input, which affects where you character will be launched when hit by a move), she gets out of the air for free with bat within (normally, characters can only air dodge and the window for hitting them out of it is predictable, but Bayonetta, if hit at the end of her air dodge, has Bat Within to let her move out of the way with less damage than the move that hit her would normally do), Witch Time being a broken counter move (if you're hit with it, you are guaranteed to die if the Bayonetta player isn't being an asshole and disrespecting you when they're playing by far the best character in the game), she has loads of options that no other characters have even with optimal play, etc
And the grand finals of Smash 4 this year at EVO had two Bayonetta players charging a move for 2 minutes instead of playing because they disliked that the crowd was booing them. And the person who won had the audacity to say they're the best in Smash 4 when half of the top players in the game didn't even go to EVO this year and they didn't play Smash 4 at all until Bayo released, which makes me question if they have any kind of fundamentals with any other character in the game (they likely don't since Bayonetta carries players, players who were completely unknown before her dumbass combos came to light in the community)
Let me say that, while all of this is true, some smash fans take the backlash way too far and by playing the character you are basically guaranteed to become a hate magnet even if you are not good at the game/Bayonetta. I really hope this winds down with Ultimate because it's ridiculous and sometimes honestly disgusting. ---