As much as I do go on about how the Emperor's Children are a bunch of femboys, there is far more to them than that.
People tend to forget (in part due to how Slaanesh has been reduced to a sex addict) that the reason they fell in the first place was their obsession with being the best of the best. All the illicit experimentation began with that goal in mind.
They (and Fulgrim) wanted to be the best, and that blinded them to how good they actually were.
I swear, if I hear *one more person* simplify fulgrim to just "yassss queen slay" I am going to break something. He's such an interesting, tragic and relatable character and I wish people didn't simplify him to "haha pretty boy".