That's not a scalable solution as not every piece of software can pay the packaging cost for every Linux distro. Maybe it's fine for core system software, but it's too difficult to expect that model to work for all software. Imagine if every website you interacted with needed to ship new website updates by packaging it and getting it vetted.
I think you still need a centralized distribution model even for things like flatpak to ensure some level of centralized auditing and revocation for software that has access to sensitive capabilities. However this doesn't necessarily need to be as large of a barrier for shipping updates as trying to package your software for a distro (and playing the game of trying to get your shared library versions aligned).
I think you still need a centralized distribution model even for things like flatpak to ensure some level of centralized auditing and revocation for software that has access to sensitive capabilities. However this doesn't necessarily need to be as large of a barrier for shipping updates as trying to package your software for a distro (and playing the game of trying to get your shared library versions aligned).