If everything is something, then something isn't a useful category. Sure, all digital design is in some sense and to some extent a metaphor for real world objects. But skeuomorphism was always referring to things that were to an extreme extent following the design language of the real world, well beyond what was required by their digital constraints or expectations of the user.

That is a useful category of visual language description that is lost when you start with all-design-is-skeuomorphism. It's not wrong it's just not a useful model for anything.