WebAssembly doesn't provide any new functionality much in the same way cars did not when compared to horse-drawn carriages. You can argue that everything you can do with Wasm can be done with JavaScript, but often it involves significantly greater effort.

Where Wasm is a massive improvement:

* Ability to use existing C++/C/Rust code without a rewrite.

* Performance consistency through languages with manual memory-management and more straightforward performance characteristics.

* Performance of working with multithreaded code by using languages that can pass pointers and avoid message-passing overhead.

* This last point is somewhat unproven as it's related to my own personal work, so take it with a grain of salt! Wasm has unique properties that allow it to be augmented to run complex, seemingly unnetworked, code perfectly synchronized between computers with very little latency in the UX. I'm convinced it can eliminate a whole class of complex networking / sync issues. I first demonstrated the concept earlier this year with tanglesync.com, but I'm currently working on a follow-up.