Companions turning around and attacking you based on their approval of you was a thing in Baldur's Gate 1 and/or 2. Kikoskia's LP of BG1-2 he noted trying to maintain a low enough reputation that his evil party didn't turn on him while also maintaining the flavor of evil he wanted which was selfish and callous, but not outright cruel and who had a particular hatred for slavers.
Lae'zel I have no trouble imagining turning us because most of the characters are, by and large not Githyanki, and she's a fairly dyed-in-the-wool Githyanki who are rather well known for having low regard for anybody else.
There's been a discussion of what constitutes an "edgelord" on the City of Heroes: Homecoming forums and it's covered a wide range. Some people have dismissed it as a label for "people who RP in ways you don't like" and in my case I view it as a case when someone is taking on the aesthetics of a brooding or gloomy character without actually making the effort of follow through that makes a dark story-arc work well. I'm not sure any of the companions really fit my criteria. There seems to be an effort made in creating their stories. Laezel and Astarion annoy me but the stories are interesting. I quite like Shadowheart. Wyll... vacillates between being amusing and just really annoying me, but again, seems to have an interesting story to him. Gale, the Waterdhavian Wizard-itis is irritating, and his story involves a rather painful bit of mechanical sacrifice I'd rather not deal with.
There's a reason I'm hoping Karlach and Alfira will be available as companions as I know my party in that case.