And… comparing Flash to V8? I'm having trouble finding modern benchmarks, but Flash is based on ActionScript, which is related to JavaScript. JavaScript has V8, which is a world-class JIT with Google's engineering talent behind it. I'd be very surprised if Flash's JIT was competitive with V8. At least as of 2011 it wasn't [1].
I didn't make any claims about Java Applets or Flash performance.
I don't disagree that WASM is faster than JS; in fact I make that point myself in several comments. My point is that WASM's speed does not enable it to be abused like Flash in a way that JavaScript cannot be, because JavaScript is already as fast as (in fact faster than) Flash thanks to modern JITs like V8. The reasons that WASM is not the "new Flash" must therefore be the same reasons that V8 + Canvas are not.