JavaScript is a language. WebAssembly is a compilation target. For this reason, I agree with you that WA can’t replace JS–unless you like to code in an assembly like language :)

WA allows us to write applications in say Rust and run it in the browser. So, it’s not WA that will replace JS it’s all the languages that will compile to WA.
And to be precise replace is not the correct word here, these languages will coexist with JS. I just think they’ll be more popular in the long run.

Think of Erlang and Elixir or Java and Scala. They are different languages, but they share the same virtual machine. I believe that this is what will happen with WA too: many languages that share the JS engine.