There's a couple of older posts (Near the beta's release) that went pretty deep into why the evil path isn't good. For me it mainly boils down to it being a typical kill everyone and sacrifice your intelligence because evil story. I'm hoping they either revamp or better flesh out the evil path to have some depth and nuance but, being honest, I'd be surprised if they actually do considering it's already hinging on you accepting having an almost literal bomb in your head and that's not an easy pill to sell.
As for evil companions I thought the general consensus was that Astarion and Lae'zel are somewhat evil, even then you can argue against it, and the rest were more or less neutral leaning towards good. Hell Shadowheart is probably brainwashed and she would've been the next closest evil character.
