> The browser standards are open and have multiple open source implementations.

The browser standards are open only in name. The sad fact is, implementing those standards are flat out impossible if you’re not a megacorp. They’re just too damn big: I recall someone counted like more than a hundred million words.

Now using those standards is easy, you can implement a subset. But the number of browser engines that actually supports enough of those standards will only decrease.

I'm not really sure for how long we will have multiple implementations. And we won't have for sure any new implementation, we are stuck with the 3 we have and can only hope the 2 non chrome ones will survive.

Browsers are absurdly well-optimized for performance. If you know how to tap it, you can make screaming-fast apps of various kinds, with top-notch graphics, font rendering, accessibility support, audio, video, etc. They also have really solid networking capabilities, as long as you don't need raw TCP or UDP. In particular, HTTP/2, HTTP/3, WebSockets, and WebRTC allow for a lot of advanced things.

By now, you also have WebGL and WASM, if JS's JIT is not fast enough for you.