I guess C2 isn't really optimized for mobile platforms just yet. But if you consider the rate at which devices upgrade and improve, and the rate at which C2 might evolve along crosswalk and similar solutions. We can safely expect that the file size and other similar problems won't be an issue after much longer.
However, if you export to html5, which is what C2 was originally design for, you get 3-8Mb programs =)
I also struggle tons with crosswalk, it gives me 25Mb apps, that turn into 50Mb after install... And these are apps comparable to other "pro made" apps that often aren't bigger than 2Mb in size. And this really hurts us as developers. But, looking at the bright aspects of it all: C2 apps using Crosswalks work perfectly in every device I've ever tested.
However, I've seen famous apps, that you know should be no more that 5Mb that, just like Crosswalk apps, are over 50Mb in size. So maybe it's isn't such a big deal (the facebook app is 170Mb btw)