No SDK or Tool has it all!
C2 is good at making HTML5 games that run great on desktop browsers. That's the main reason why I bought C2, because I wanted the option to make browser games.
I don't expect HTML5 games to fair well on mobiles by today's standards. I use other SDKs to produce Native code on mobiles, and it would be very hard for HTML5 to beat that, at least for now.
HTML5 is great for doing mobile utilities and productivity applications though.