Then why can’t all the times Kylo isn’t being unquestionably evil just be thrown under “Ben Solo?” Why couldn’t someone say; “it wasn’t Kylo feeling the call of the light side, that was Ben Solo momentarily showing through. Kylo is 100% evil.”
There is no indication that the First Order (apart from Snoke) knows who Ren really is. And Kylo Ren only admits his call to the Light to the shadow of Vader and to his father; and his father calls him Ben, not Ren.
And besides that, we’ve had at least 4 unquestionably evil characters in the franchise, 2 in the OT alone; why would you want another?
Yes. That’s the way the Dark Side works.
You don’t think it’s been played out?
No. Star Wars is fantasy. It’s also a longstanding franchise with certain tropes it has created for itself to follow. To stray too far from them is to not understand what makes Star Wars what it is. This is why so many longstanding Star Trek fans hate Star Trek: Discovery.
Personally, I think if anything the “there is no good or evil; everyone is flawed” trope that has been popular lately (The Walking Dead, Battlestar Galactica, ST:Discovery, Game of Thrones) has been overused.
JEDIT: Oh, and Star Wars has had more than 4 evil dark side characters (eg. Asajj Ventress), if you include The Clone Wars or Rebels.