I agree, when it comes to pure HTML5, as in putting the games on a browser, C2 is King, Queen and the rest of the royal family. But for everything else, seek a different engine.
After I finish my game I'm switching to GMS, but I'll probably keep C2 for making short demo versions that people can try over the net before they decide to buy my games or not.
Everyone would have switched to Unity or GMS if it were that easy. Thing is...how many of us can create games of the same calibur using them? Even then I find the workflow to be completely bonkers in comparison. Seriously - go check out how to create and animate a simple sprite-based game character. As for GM...it's an incredibly buggy and obtuse piece of software if you ask me. I am truly baffled by how popular it is.
About GMS being buggy and having bad workflow; I guess that's why Construct 2 has so many games to showcase! It has.. um.. Erm... Oh yeah, nothing. Same as GMS, except for Hotline Miami, Steal Bastard, Spelunky, WizardWizard, Wanderlust: Adventures, Risk of Rain, Gods Will Be Watching, Top Hat, Metaloid. Oh wow that's actually quite a lot, and that's just off the top of my head. Even CC has more games (like 2, The Iconoclasts and Minitroid).
As for making a simple sprite-based game character, I've done it before in Unity with the help of a tutorial and it wasn't hard. As for GMS, it made more sense than C2, an object is supposed to have sprites, not the sprite be an object itself. Unity does this as well.
I don't see why you think GMS is bad and hard to work with, I've made a couple small games with it and it's completely fine.
Also the community seems a lot better and more mature than C2's one, I've seen complete engines being shared and thrown around. I myself scored a Metroid Zero Mission engine for GM8 (that can be imported into GMS) that's 3/4 done and a 2D Minecraft engine. Considering this is easily able to be exported to PC natively, it's a huge improvement over your ZM engine that you did in C2 (which I remember begging you to let me see for like 4 months).
Meanwhile everyone on C2 forums hoards their engines like everyone is a thief.
C2 is basically the next generation of flash, it should be used for browsers only, or very short demos. But by no means for a full game.