WASM does not run on the same VM as javascript, or rather, that V8 happens to provide the facility for both, does not mean that much. They are effectively separate things. Now, if you mean to say there's some degree of interop via a chunk of memory between the two, then fine, but that's not particularly an advantage.
WASM is a bit different between browsers, it's not 'stable'.
That said, Applet/JVM are 'nowhere' these days and would require specific installation.
WASM is not 'faster to start' and it's not even 'fast' <-- this, and lack of clean interop is the worst thing about WASM. It's slow! If you combined the fact you have to go across an ugly 'bridge' between JS and WASM to do almost anything, it's probably not worth it for performance gains, and certainly comes with major dev. cost.
'Targeting more languages'? Really? Java, Swift, Python, Go - not really. You can target C++/C and Rust but only in very specific ways.
So the advantage for WASM would be 1) security for user, but in reality v8/JS is already secure 2) performance, but in most cases it's not true 3) 'hide your code' yes, this is nice for some algs. and 4) port your C++ algs to the browser like Photoshop/Autocad.
So far the reality is that it just doesn't fully add up.
Maybe some day.