Karlach

Enough said was already, but just another small tweak that won't require much (re)-work: they needs to fix Wyll offering to take Karlach back to Avernus over the player. If the player doesn't offer Karlach to go to Avernus together THEN and ONLY THEN Wyll should interfere.
Some relationship-meter related checks can be added. Like, easy check if relationships are good or perfect, and no check at all if the player romanced Karlach. Failed check or choosing other option would result in Wyll's offering his hand.

I honestly cannot comprehend why it's not implemented like this right now. It pisses me off even more than her ending itself. Wyll, get back, nobody asked your opinion! I am not sure, but Wyll himself may not be the reason. I guess if he is not in the party, you cannot take Karlach to Avernus unless you've romanced her. Thus solving this problem just means connecting our options to relationships and dialogue choices, not to romance. Especially, even if I haven't romanced her, I had our relationships on max, she told me that she loves me (maybe as a friend) and adores me, surely she would rather go to Avernus with me and not with Wyll.