I mostly agree with those points.

Flatpak does support sharing ‘libraries’ (although not in the way you mean), however from my perspective the main problem is developers referencing Kde-Framework-420.69.1, and others referencing Kde-Framework-420.69.1-rc1 or various other variations of very similar dependencies, which tends to eat up additional disk space. I’m personally not too bothered by it, but that’s only because I have the storage space for that.

With flatpak’s shtick being isolation and a consistent runtime environment, I doubt there’ll be true sharing of linked libraries and the associated memory space, so excess RAM usage and disk space as you’ve mentioned.

The distros based on Flatpak (can’t remember the names right now sadly) are mostly immutable ones, where the base system remains untouched, and in that scenario I think it makes the most sense, particularly in education.

The instances I use flatpak are slightly similar to that, with the difference being the libraries available in the base system may be too old to run the application natively