Yes, it applies to Ordinals but not Runes AFAIK....

As a numeration system dependent on a protocol that exists independently of the Bitcoin Protocol, its as real as you want it to be.

Some may say its arbitrary, and you will no doubt get the usual Ordinals Deniers coming into this thread saying none of it exists at all.

Personally I don't really care about the "rareness" of sats. There's already so much "value" being created on Bitcoin outside of its original protocol that collecting "rare sats" doesn't appeal to me. But if there's a market for them, and people find them valuable, you can't stop collectors/flipeers from assigning value to them.