I've been having similar reservations about c2... The only thing stopping me from jumping to UE4 was the lack of integrated bones animation for 2d. But yesterday I found a programme called Creature which is amazing that I must check out. Way better than Spriter....
I read on Unreal forums that Unity is much faster at animated sprite rendering than UE4 with Blueprints, so UE4 is not perfect... but the limits are way out there. Stuttering simple 2d platform performance in Umbra is depressing, with reasonable performance limited to high end machines, so I feel your pain and have been looking at other options for a while as well. I think I'll finish my current game experiment then I'm done here too. I'll be back to check out c3, so I reserve judgement there. Good luck!