C2 biggest advantage is that it has a quick implementation of features (usually each week) because it uses javascript, and its biggest disadvantage is that its not native because it uses javascript.
Do people test their apps on a mobile device as they develop? Its probably a good idea.
You can't compare successful apps on unity to C2, because a gazillion people develop with unity and relatively few (serious developers) with C2. Angry birds could have been written using C2. Its usually not an issue of the ability of the development tools, but the ability of the developer.
IMO, Scirra should hire 2 or 3 more developers and double or triple their feature output each week.
Ashley maybe a gpu usage monitor could be added to the debugger, so people can tell if its the graphics or processor slowing things down.