Fedora packages versus upstream Flatpaks

This definitely isn't true; there's typically some internal distro process that delays things (eg promoting from updates-testing to updates).

At the same time, even when getting the binaries straight from the browser maker via their automated update mechanism, the updates aren't pushed to everyone simultaneously either; there's typically a staged release.

Even then the delay between the packages/binaries being available to when they're actually applied (whether the binary comes from the distro or the browser vendor directly) usually requires the user to acquiesce to having the browser restarted, and IME is typically the longest pole in practice.