You can't really compare C2 and UE4. Yes they both can make 2d games for most platform but here similarities ends. You need a bit more knowledge how to do thing, to make simple games in Ue4 than in C2.
I am not comparing engines, I am comparing their workflows and the ratio dev speed/optimization.
Not really. You need more knowledge on how to do things in Impactjs, but UE3 is still an event based system. Once your brains can proceed the algorythm you just have to learn the soft, and that goes for every soft. And i won't go for a UE4 for 2D if I don't really need it. To be honest I don't see the point of even doing this when more reliable and stable solutions do exist.
Each time they update Paper 2D or their version of UE4 something breaks in my projects.
Unity is still the most reliable and effective option for 2D games if you want to go pro and have full control of what you are doing.
But yeah we can't really compare. But we do.