The thing is, our team has extraordinary breadth so everyone's good at some things more than others. What matters (and what we select for) is curiosity and openness to learning.
I previously worked on distributed systems with lots of immutable state. Here I've learned tons about distributed systems that have lots of mutable state, and it's made me realize immutable state is easy mode.
Wouldn't this person be put on a PIP and then fired if their performance didn't improve?
Even at companies with non-uniform salaries, it's difficult to down-level someone. Their morale will drop, the team's anxiety will go up, and (if they were genuinely bad for a long time), the team will wonder why they weren't fired.
But what if in a year or two a person is not so great anymore? Just by my own past work experience at 2-3 companies, there were always some colleagues that were definitely not good at their job (and this was pretty much common knowledge, multiple people had the same opinion). Maybe they were good at the beginning, or not even then. I would have felt it to be super unfair for them to get the same money, or the same salary bump as me.