Part of the reason for shipping ‘simple’ apps as snaps was to test the whole infrastructure of seeding snaps, maintenance of them and the upgrade process from Ubuntu release to release. Ideally it should be transparent to the user what packaging system is used. So if it’s slower in some circumstances, that’s really a bug and should be fixed.
It’s entirely possible that larger, fast changing applications may switch to being snap by default in the future, and Libre Office seems like a good suggestion, before that happened, we needed to prove that everything works with a much smaller, less critical set of application.
Indeed the very first application to be seeded was in Ubuntu MATE and was pulsemixer. An application that almost nobody will use, but it was needed to bake something small into the image, so we could test the process.