We can argue all we like about the tech and why it's this or that...
If the game you want to build for your target platform does not perform as it should on the client machine you are dead in the water. End of story.
The customer sure as hell doesn't care if it's HTML5, C++ or freakin Basic.
Well, let's talk about realistic expectations then. C2/C3 are HTML5 game editors and people should only reasonably expect that games made with it work really well in browsers. That's what it's made for.
People have unrealistic expectations that games made in HTML5 will work flawlessly on other platforms, in part and understandably because that's a promise Scirra makes on their homepage. "Publish Everywhere" is misleading at best and doesn't explain users will need to use third party wrappers. Exporting to other platforms has never been easy with C2, in my experience, and it's still promised with C3.
Ashley has said they plan to build their own wrappers for one of the platforms, maybe all. If they do it well, what does it matter how it gets on a certain platform as long as it works well. Promise kept. We'll just have to wait and see.