I do see your point, but the "take the place in Avernus for herself" route is hardly in-character for her, no matter how you slice it
General revenge - maybe, sort of (although it doesn't really satisfy her, as Gortash shows), but power doesn't seem like her style. And I wager none of us really want to see the character herself re-written - we love her for a reason, and her being different from the other companions in terms of her struggle is part of that reason, I think.
I'd say in her case the routes should me more equal in terms of "likely to happen", rather than reasons.
As in, I'd say the 'best' option should be hard to get and easy to miss or screw up, so that the 'bad' routes still bear significance. Well, that - or maybe the price should be steep, so the player theoretically has motivation to NOT go that way?