[astrobe_]

The material difference is that this editor is an order of magnitude smaller than a browser. Sure, you can go "we have plenty of RAM/storage/battery these days", but consuming 10x more of every resource you can think of is quite the hint that you are not using the right tool for the right job, or that you do not employ the right person for the right job.

[SahAssar]

That's not because of JS or WASM, that's because of the browser. Using JS or WASM does not mean you need to use a browser, you can for example run quickjs, node or whatever other runtime without bundling a browser.

This editor could have been written in js and use the exact same libs for rendering. If it used one of the smaller js runtimes (like quickjs) I'm guessing it would have been similar in size and pretty close in performance.

I don't get why you are conflating using a certain language with bundling a full browser (like electron does). It's two completely different things.