Yes, this is definitely a difference in how we perceive the language. I don't see any inherent problem with a lookup table in the language, given that most of the language is already lookup tables in the same sense (what distinguishes 'couch' from 'chair', for instance). And it would not occur to me to have a rule for "*nouns" rather than the actual separate rules for nouns and pronouns. Note also that pronouns have possessive adjective and possessive pronoun forms, while nouns do not. They're an entirely different sort of animal.

So I would not think to write "It's brand is whichever brand is it's" instead of "its brand is whichever brand is its" anymore than I would think to write "me's brand is whichever brand is me's" (or whatever) instead of "my brand is whichever brand is mine"