I don't feel complaining about being paid under market rate is a strange thing. 20% raises are not ludicrous in any way, if this prevents an employee from leaving.

I didn't say he should have stayed, he did the right thing, but going in at x and expecting x+20% in six months is ridiculous. If he was expecting that then he should have got that pecific number negotiated up front.

The company has more information than the candidate when making salary offers. If they negotiate in bad faith, that burns up goodwill. It's their decision to do it! I've never heard someone ask if their salary is in-line with the other members of their team (adjusted for performance/experience): it's a given assumption that _the company isn't going to pay you massively less than your peers_.

Plenty of companies do, because HR does the negotiations & their motivation is to minimise employee costs. If you're not negotiating with the recruiter/hiring manager, you're likely to get a poor offer.