There is some true points in this, but you can not generalize. For some people code might be easier to maintain, for others the C2 way is more clear and manageable. And if you talk about really big projects, they can become a mess in pure javascript or another framework like phaser (for we stay in the html5 content) very fast, too. Only because for you code is more easy, doesn't mean it must be for all people. (And i code long time in all kinds of languages, so i know the other side). Anyway, i think C2 is perfect for small and middle projects, but an experienced developer also can handle big projects with it. Everything has it's pros & cons, some things are more hard to do in C2, others are lightning fast to set up, and like i said before, everybody need to find out on his own what he/she prefer.
And really, comparing unity to c2 isn't really fair. This is like comparing Photoshop to Paint.net. C2 is more for the solo indie developer or small teams, that can make big projects with it in their scale, and Unity is used by the big players and teams with 20 or more people (not saying one man can not use it to make his dream game).