Yup, it's all about DNS and links.

But let's try to look more than a few years out for once? OKAY?

You could make a very decent web that is made out of many clients, that can all link to each other and maybe even all run in separate tabs of the same browser (or whatever 'process' model you want).

But god help you 50 years down the road when you need to download new client browser for every other web page.

This, among other long-term type trade-offs are the very good reasons why the "open web" as it exists on it's current trajectory are a very good idea.