What a fantastic story! You’ve really broken it down carefully.

Did you know that for personal pronouns, some languages like Greek have a singular, a dual, AND a plural? So you end up with three pronouns instead of two in the number category.

And nobody ever blinks about the fact that English is not one of those languages or claims English grammar is therefore deficient or inferior. Ditto with respect to languages that don’t differentiate personal pronouns by number at all.

Grammar describes how people communicate. Languages change, and grammar rules get updated to reflect those changes.

Not a big deal. People are more important than arbitrary speech rules.