I miss the good 'ol phBB3 days...
With regards to C2, as an editor it is overall ending up better than CC, although i haven't used it much yet. There were little quirks working with animations and the like that i haven't gotten entirely used to yet. The audio implementation is also feeling far inferior as it is now, which is some html5 limitation at the moment i think. Then theres the problems with some features being missing, per pixel collision being a big one. last time i checked there's no alternative similar to the canvas object in CC either (to do texture modifications during runtime). distortion is completely feasible in html5 so im sure that will come soon enough. The editor is truly leaps and bounds ahead of CC and the program is way more polished.
With that said.
CC is definitely executing lots of math faster than C2 can. Displaying sprites might be more effecient, but doing anything useful with them isn't, at least from my small experience with C2. CC just feels tighter executing something with a lot going on, and i'm not sure why, but i do admit i need to play with C2 more. My problem is, i really like using per-pixel collision and distortion and lots of big expressions running everywhere, and C2 isn't handling that like CC at this point. I hate that CC games are hard to get running on some machines and i hate that CC runs on windows only etc. There are little bugs i encounter when messing with some plugins or family stuff in weird ways but they've NEVER been something that got in the way of my development of anything at all. I just wish C2 could get some OpenGL windows/mac application exporting capability so per-pixel collision and canvases and lots of expressions were as feasible as they were in CC (Likely they would be much more so since C2 is so much more efficiently written).
As things stand, i really like to use CC because i can make some really cool stuff with canvases, per-pixel collision, xaudio2 and distortion. I've even written some pixel shaders that can use the canvas in a feedback loop to simulate mass particles on the gpu through a texture/effect that you paint into. dunno if i could do something similar in C2 yet but i'll try soon. I have no qualms with C2 aside from those things. Its really an amazing piece of software and for 95% of the people who did use CC, its entirely better. theres still a few of us around however who like pushing lots of limits and have hit barriers with C2 that aren't so easily reached in CC at this point in time.
Spectrum Wing by my brother is another "simple" game that would be impossible to make in C2 because of the dependency on canvas and per pixel collisions. If you were to say you could make everything in c2 that you could in CC you would really be mostly right. you can make pretty much any SNES game, and any game in that vein, it's just as you move into more fringe requirements that it falls off, and that's why i recommend everyone to C2 if i do bring up Construct somehow.