That may very well be the case, but there's also the scenes when you cut between characters that shows Trevor doing stuff just because it's the thing he would do. Burying a body in the middle of the desert. He's clearly just killed someone. Maybe it was a biker, maybe it was just some unlucky soul he ran across. Or tossing a Lost biker off the bridge in Los Santos. Or Trevor jacking it in his trailer and wiping his hand on the wall. He might be putting on an act to be seen as the most unpredictable guy around, or it may not be an act. Or somewhere in between.
And with Michael, they are always at each other's throats the whole game. I think Michael says stuff like Trevor is a hipster just to get under Trevor's skin. Meanwhile, Trevor keeps calling out Michael for being the hypocrite he is. A great example is when Michael is stuck in the trailer and Franklin is tracking down the last members of the brothers Trevor was killing earlier, Trevor flat tells Michael that he doesn't appreciate Franklin despite Franklin risking his life out there for Michael and Michael supposedly taking Franklin under his wing. Even Michael has to take his in and says "that's fair." I mean, what else is he going to say? That Trevor's wrong?
I think Trevor is one of the most interesting R* protagonists simply because he doesn't fit into a solid category and maybe/maybe not is a posturing wannabe psychopath. Here we are still discussing him almost 15 years after GTA5 was released, so R* did something right with him. It isn't like we're discussing Claude or Johnny K very often.