The problem is that the browser is so good at being a ubiquitous, open-source, open-standards-based, cross-platform, near-instant-loading secure remote code execution environment. As Brendan Eich says, always bet on JS and WASM. I would extend that to -- always bet on browsers.
With the amount of change that has occurred in browser technology over the last 30 years, I strongly think the future looks like more improvement in browser technology (and perhaps deprecation/removal of old standards) than an entirely new paradigm. I know various early web pioneers want to build a post-Web application delivery system (notably Tim Berners-Lee and Douglas Crockford), but given the accumulated legacy of modern browsers and web apps and the ongoing investments into browser technology, I don't see how any post-Web system could gain any traction within the next 25 years.
But yes - your point still stands. If anything better than browsers ever appears, the internet will indeed still be there to host it.