80/20 doesn’t mean literally 80% and 20%

It’s just a rough way to say “mostly this with a decent bit of that” because 20% seems like a medium-small percent that could or could not matter depending on the context

That’s all anyone means when they say 80/20

To your second point, the 80% could be lots of basic things and the 20% could be the important facts, so it’s not always meant as a dismissal that the 20 doesn’t matter