but weirdly, when negotiating for someone else manage to get just as much pay for their friends as a male negotiator. Lack of union representation in the modern workplace is ofc a big factor: my wife's work for example is a Unite shop where they always get a decent pay rise.

In my industry, software developers usually switch jobs in order to get better pay, and there's very little union representation, so the salary you negotiate in the interview is usually what you're stuck with until you go. 18 months to 2 years is the normal tenure where I work.