Not the worse I've written out of boredom, but I wonder, how much terrible I can make it...
At the end of the day, the most effective way for the fireflies to make sure they get Ellie was to simple spoil part 2 to Joel, and letting him know how terrible things would be should he save her
Bro would've retired so much earlier, spending his time with Tommy as a loved brother and part of a community while Ellie got her dreams of being a brain stuck in a jar, watching as Abby becomes even more massive from a shelve like some kind of creepy lava lamp
With spoilers everyone wins
Femboy/girl original Quin is an easy fix, just let Tollus use his magic when learning from Quins betrayal (we don't see any other cultist run away, let's say by that time everyone was enthralled by demon magic but him), now he's turning into a girl but instead of doing it like Brianne we go slowly, fem Quin is far more vulnerable and transformation magic doesn't seem to help as the source of his corruption is beyond regular means. The rest is slow corruption type magical camp, let's say, a way to explore this new side of him that was there before. With a good writer, it could be something great
In this scenario Quin worships you as you become a source of comfort, either by pushing his corruption, lets say, full slutty bimbo, or a more measured way, so he becomes more soft and honest to you, and, sharing a similar path to girl Quinn, he actually wants to help and goes out of his way to help
This is another easy fix, original Quin waits for you to buy equipment because no one likes him, when a truly grateful Quin would've tried anyway, and you stop him as he has no way to actually help you