Html5 isn't really limiting in terms of making a large game. I've been working on two large RPGs and c2 handles then just fine (other people have been working on large games too, like C7 with Courier). Now that we have crosswalk and Ejecta for android and iOS exporting, both of those have memory management so you can make large games for mobile too.
Html5 does have some downsides, but they aren't enough to really keep away from C2 except in some very specific cases, like needing every drop of power an older mobile device has. It also has some advantages, too.
Html5's main problems that I've experienced:
- Game logic speed isn't as fast as native, but it's still pretty fast. On PC it is very unlikely you'll hit any problems, however on older mobile devices like iPhone 4s and earlier it's quite likely you'll run into them (iOS is worse than android in this regard because of not allowing apps to use jit). C2 on PC has been able to handle almost everything I've wanted to make with it at 1080p/60 fps, and that's on a computer that's most of a decade old. That of my ideas which it isn't able to handle at 1080p60 it almost does (at about 30-45 fps) and would run fine on a more recent computer. All game dev tools have limits though.
- the node webkit export is basically chrome, and the chrome team decided to drop all support for hardware acceleration for XP and vista. This is seriously annoying, but can be worked around by starting the game from a shortcut with a flag to disable the gpu blacklist. Doing so works fine on my vista computer. It's likely that the person you mentioned who tried to make a tower defense game was getting software rendering or was doing something wildly wrong with their events, because c2 can definitely handle a tower defense game with way more than a few enemies.
Really, when it comes down to it, c2 can make pretty much any game you can imagine as long as it's 2d and within reason, of course (hardware has limits even if you were coding in assembly, after all). All the main big name tools can make great games and the main consideration for what tool to use should be what works best with your own workflow. I don't like MMF or game maker, but I respect the opinions of the people who do (for what it's worth, the person making the game you cited, the iconoclasts, left MMF for CC. I know he's had problems with CC - and I did too - but c2 has rectified those issues).
Try 'em out, see what you like, but be sure to give them a fair shake to make sure you don't get a false impression (for example, the performance of any game made with any dev environment, even in assembly language, can be crippled with a few incorrect lines of code).