Your use case sounds very much like an edge-case in websites. Of course highly customized animations and weird out-of-the-ordinary UI elements are going to be an extra pain in the ass. I have no doubt there are customer requests that simply can't be fulfilled with HTML and have to be done in WebGL. The fact is, most sites are "fairly basic" and only really need HTML, CSS, and a little javascript to accommodate the vast majority of use cases. I'm glad you're doing complicated things, but that doesn't change the reality of most web developers.