The borderlands games ruined me now I keep wanting shooters with loot and boss fights how can I undo this
What's wrong with wanting to play a certain style of game? I would think that if you want it, you enjoy it. No?
In any case: just play something you would enjoy. If other shooters have lost their appeal, don't worry. It'll come back to you (I've "burned out" on quite some gametypes from time to time. I just broaden my horizons and play something I otherwise wouldn't play. There's quality in all genres).
As for shooter suggestions: the already mentioned twitch shooters (btw: how is that new unreal tournament shaping up?), devil daggers, superhot*, tower of guns, shadow warrior, wolfenstein: new order. Hard reset isn't bad, but nothing spectacular either.
EDIT: almost forgot: should it be
first person shooters? If not, I've got more suggestions: enter the gungeon*, nuclear throne, risk of rain or even good ol' bullet hell shooters like jamestown, ikaruga or sin&punishment.
*I have yet to play these, but I've heard very good things about it