It's not really a "WASM problem", as such; you can use the DOM from WASM and that works quite well. Similarly, you can do all this kind of graphics drawing with just JS as well.
It's just a choice this framework made. I bet there are actually some real advantages to it, but also disadvantages. I very very much like the customizability of the web, so I'd be very surprised if the advantages would outweigh the problems.
In short, I don't think it's really the same as Flash.
