I kind of agree, but I'm not sure if it was aimless. I do think that we didn't get anywhere in the second season, as it started and ended in the same exact place, but I think the story they told and the characters they created were good enough to give it a pass in that even if it didn't go anywhere, it was a good story in itself and contributed to the world building. I will agree that the violence and grotesque aspects were the weakest parts, and probably needed to be toned down as you become numb to them after awhile with the worst being how rapidly cave girl just explodes for no reason.
I think that's why I don't really get it, it feels like it's a different show that they wedged into the series, but it's also good enough that I don't mind that. Though the weak aspects of the series really show through in the second season and I hope they pull back on them if there's a season 3 as there's definitely creativity in the show as a whole.
Edit: I think that in a lot of ways the season can be viewed as filler, but I also don't think filler is bad if it's interesting in itself and tells its own story. Maybe it's one of those things that best kept to an expanded universe, though that's usually a failure, and my enjoyment of the Second Season comes not from the show itself but from what the season was in itself, which is why I'm conflicted on it.