The restrictions are very logical when you break down the target platform. C2 exports mostly to JS. You'll have the same limitations (download speed, scripting speed, etc...) Most laptop and desktop browsers can handle a large amount of stuff very easily. Even without implementing WebGl they can handle a lot. Mobile browsers, not so much. Tons of objects and particles will make mobile browsers crawl. But they weren't designed for game playing, they were designed for media consumption. CacoonJS and such will help with that and it speeds up the code a lot, but it still won't be as capable as native java and dalvik (or ART) nor machine code written in C for Android or Objective C on iOS.
Depends on the tool for the job and your game you're trying to make. Keep your restrictions in mind. If you're doing mobile, keep it simple. If you notice, very few mobile games have tons and tons of detail anyway. There';s a reason for that. If you're doing desktop, keep in mind age range of hardware. I know my laptop can handle an awful lot of objects, collision calculations, particles, and everything else being thrown around on the screen. My friends 6 year old laptop with an old Cele and Intel GMA can handle most of that minus webGL stuff.