It's just that when people compare this to Linux vs Windows\MacOS - the correct comparison to what Mozilla is trying to do would be ReactOS vs Windows. Where's ReactOS? Right.

Arguably since mainly what people actually want from the Web is just a cross-platform document renderer/UI system,

Yes, most customers want that and it's rather cheap to develop (not being childish, look at Gemini again, it just should be repeated with the same means, limiting extensibility of the standard, and different goals - one, more rich markup, two, some way to replace Flash of the olden days and\or the script nightmare of today without allowing the replacement to grow into a similar monster, three, some degree of content-based addressing, like in P2P, so that CDNs and big platforms would be less important, four, something to replace the centralized PKI system with all those wildcard certificates sometimes issued to bad guys and everybody saying oops).

People who want the Byzantine nightmare, or the ad-stuffing system with some websites existing today, are all on the other side. Only if the ad-stuffing system isn't really required for what we need to do, then those people should lose the competition and go bankrupt. I hope I'll see that happen.

but I somewhat suspect we’d end up with something better and easier to develop for than the Byzantine nightmare that is the web.

That's certain.

Network effects would limit growth, but I think as the web gets shittier and shittier there would be growth.

There absolutely would, especially in the times of "there's an app for everything".