Okay stop, you clearly don't understand the mechanics/realities of Eora.
Iselmyr is not "someone else". Iselmyr IS ALOTH. He awakened to one of his past lives, this happened because in his current life he was not standing up for himself so his soul proactively did what it had to do to protect itself.
If people get Aloth to come to terms with Iselmyr and face up to the reality of why she happened, shocker, he starts standing up for himself, and actually can be a bit of a "meanie" (really Obsidian, that isn't even a curse word). There are scenes in my Deadfire game where he outright insults Pallegina/Eder calling them names and or stupid. In fact, he is far ruder and condescending to them than they are him. So again, he is the same person as Iselmyr, if you teach him to stand up for himself anyway.
Why anyone would choose to keep her around is beyond me, because it just means Aloth as a character does not grow.
Lastly, more critically, has anyone even gotten this so called Eder/Iselmyr romance to happen? There are data mined game files, that's nice, but any search of google on this subject only leads to this very forum where people talk about data mining it. No videos, no threads where people discuss it happening in their game, no one talking about how they got it to happen. Data mined files aren't real, because they might be "in the data" but they don't exist "in the game".
Though I do agree Obsidian (and game Dev's in general) should do a better job of removing files/data that are not used in the final product.
Maybe they left it to troll us. Who knows, the next thing people might find in the files is a romance between Worthless Idiot and Ishiza.