In my experience, there are some things that just don't work consistently on mobiles in HTML5 - with or without the use of cocoonjs, crosswalk, chrome or whatever. This is some of my experience using C2 for mobile (which was what I bought it for, discussion about viability of 3rd party wrappers aside):
1. Physics. Collisions cause browser hesitations even in my quad core super mobile (I have an LG G, a Samsung S2, iPhone 4 and Toshiba Excite for testing). These hesitations change the characteristics of the physics objects (how high they bounce etc) enough that a player A could do or see things that a player B on a different phone might not. Games using physics on mobile are not viable unless you don't care that different players might see or do different things. I do if it changes the game play...
2. Platform. Same as 1 but to a lesser extent. Any browser slowdowns cause changes in how the behavior appears so that the player's experience ultimately depends on something I have no control over - what type of phone they bought.
C2 and HTML5 do other things well, but these are the weakest ares I think. Even my flappy bird clone runs differently on each of my test devices and that only uses custom movement! If I test anything made using Unity then these problems of handset performance and compatibility don't seem apparent...
Edit:
EddyDingDongs, not everyone owns a top of the range android / iOS device like yours and I can't ask my potential customers to go and buy one before downloading a game. If everyone did have one already then there would be no need for this thread...