The flatpak size disadvantage is negligible in the age of terabytes
the issue is overstated as most flatpaks use the flatpak platform runtimes and share their own libraries in a similar manner to the host, yes its separate libraries, but its not dozens of disparate copies like some detractors of flatpak seem to state
that’s the beauty of distros, those that want traditional package structure can still use a distro that does.
Even the current flatpak first distros like OSTree spins of Fedora (Silverblue, Kinoite et al) provide mutable containers for using any package format you like.