Afaik snaps can’t share depending packages, making it store the same dependency multiple times. Flatpak can share the depending package+version, sharing it to every app it needs and store it once.
The Golden advantage I see is not having issues installing multiple versions of the same dependency, which would be kinda hard for a native system depending on the type of package an app is depending on. Like Python and Java could easy have multiple same versions on a native system, but other things may be too difficult to realize except you use Flatpak