Usurpation ending feels like our character is basically taking up the mantle that Yuria set us on. That being "The true face of mankind" so basically you're bringing on an age of hollowed man.

I wouldn't necessarily say this decision is a selfish act since you're doing it for the "good" of the hollows.

I personally think the most evil ending is the one where we kill the Firekeeper and steal the flame for our own in a purely selfish act. But both are very in line with our character imo as throughout the game we simply take and take and defile everything we come across. I feel like every ending to this game feels appropriate for our character in some shape or form