No, it isn't. Games are already served by consoles first (which obviously won't run webasm), and steam second. There's no market there, and it's already one-click to launch steam to the game in question. Where it will then download in a medium suitable to handling the downloading & updating of a game's assets instead (which, even for a demo, is in the gigabyte range - you aren't lazy loading this).
As for 3D applications what 3D applications? Do you really think Maya is going to be ported to a browser? Why would they bother? Why would they restrict themselves like that?
The web has no advantages in this space, and the needs of those markets is already being served with superior technology and infrastructure.
Flash games are dead and even facebook games are largely a thing of the past as Facebook is now primarily used on mobile. The casual audience is on their phone in app stores & not on the web anymore.
I assure you those casual game companies are not going to want to go anywhere near vulkan or similar, though, and they are generally fine with the performance scripting languages already give them (hence why they were in flash instead of java applets)
They want strong 2D graphics capabilities primarily, which is largely an ignored category. <canvas> has a 2D context, but it's pretty crappy.
Most web-based games will probably remain to be in 2D (for multiple reasons, including development cost and accessibility), but 3D games on the web are certainly performant enough.
To give one example, bananabread is a tech demo showing off what can be done with asm.js and WebGL (performance is likely to get even better with WASM):
As for whether a VM has an overhead compared to native, of course it does, but you're not going to convince anyone of your viewpoint by stating something that's already obvious to us all. The performance of web-based games doesn't have to be the best, it just has to 'good enough'. I personally don't think we'll fast adoption of WebVR, but I'm glad it exists as it helps to have it as a goal to improve 3D performance, almost certainly leading to reducing the performance overhead of browsers (as low latency is a key component of a good VR experience).
C++ or Rust -> wasm bytecode is great. Soon we'll be writing directly to command buffers, no fuss.