> Afaik wasm is just an abstraction on top of a jsvm

it is, but as a compiler target there's tons of opportunity for automatic optimization -- in my experience wasm (from rust) tends to be faster then then hand-written js for the same function (although, i'll admit, javascript is far from my strongest language, so take that with a grain of salt)

Wasm objects are what you get in C or other low-level language, with a linear heap and zero metadata. That alone makes it vastly faster and easier to JIT than JavaScript.