You might be interested in this recent blog post where we noted on some hardware setups our HTML5 engine could actually beat the performance of our old native engine:
https://www.scirra.com/blog/102/html5-games-faster-than-native
So I don't think there is any problem with HTML5 being fundamentally limited in performance - it's just whether the quality of the implementation allows it to reach its full potential.
Your framerate on Safari iOS 6 sounds unusually low - perhaps you could share your .capx so we can take a look? Our Space Blaster demo game can average 45 FPS and rarely drops below 30 FPS on both an iPad 2 and 3, even using retina mode.
A good way to monetise HTML5 games at the moment is to contact game publishers and sell your game to them for their use. Sites like MarketJS are helping make this happen. For larger games you could also consider using the Javascript SDK to plug in your own payment system for IAP in the browser.