From a story perspective a possible evil path would be for you to realize the huge power potential behind the Cult of the Absolute, and join it if only to take control of the whole organization. It's quite simple, but it also requires some gameplay advantages to make this path more convincing. For example the tadpole powers could only be unlocked by joining them. That could make up for losing out on companions. In fact, they could make a proper evil path with minimal story changes, just by shifting some of the rewards and powers you get on the normal playthrough. Almost everything is already there. The problem is that they don't dare to keep anything of great value (like the tadpole powers) outside the "default" path.
