Sounds like you just gave an arbitrary line where difficulty is suddenly considered unreasonable.
Completely optional content can be as difficult as it wants. There should be extreme challenges you can choose to face. You don't have to fight her.
The fact is plenty of players welcome and enjoy the challenge, and learned to dodge her moves. Just because you find something too hard doesn't mean it needs a nerf, especially if it's optional.
And on your bed of chaos point:
It's not optional.
The skillset required to beat it is different to what is used to get through the entire rest of the game. In malenia's case you beat jer the same way you beat any main boss, except you need to do it better.