Well, by the sounds of it, you don't seem to be entirely experienced in all of this. In terms of making a good looking platformer or pixel game at all, Unreal is not really the way to go unless you want to put a lot more time into it and even the visual scripting is more difficult to comprehend than Construct 2's. Construct Classic has actually had my attention for a while, as I'm an experienced programmer. As for what you can do in Construct 2, it's practically unlimited. You can use 3D graphics, and to be honest you can do just about anything you could do in everything else. WebGL is just a web port of OpenGL, which is DirectX's rival, and is actually a lot easier for rendering graphics. Hell, get your hands on a programmer and they could even program in DirectX, though that would be a waste, DX is much slower and doesn't seem to have anything to beat OpenGL and WebGL. I would check out the possible things you can do with HTML5, as that's the programming language that Construct 2 uses.
But, Construct 2 includes basically everything to make a game like the one you linked, it wouldn't take long to duplicate it. The designers here just chose to make games differently, they design games mostly on what they think sounds good, which is okay of course.