My team at my company has been interviewing people this last half year: we've extended offers to a few and so far each has chosen to work elsewhere because they found better pay.
At the very least for the last half year, I think developers may have an "upper hand".
I see this as a bad market though too. Many companies paying bad comps and making people jump through a lot of hoops to get a decent offer.
I had to get no less than 6 offers before I got one that was reasonable in my last search. 6. I had done about a dozen onsites and dozens of phone screens at that point. This was just a year ago. I expect the same this year - if not worse because of the market doing so poorly.
> each has chosen to work elsewhere because they found better pay
The candidates don't control the comp you offer. Claiming that those darned candidates have the upper hand because everyone else pays better is a bad faith argument. Not that you can tell your boss that, I'm sure.
Supply and demand, in net terms it depends on externalities, but when you're sitting down in an interview with a candidate, you're setting the tone/pace for them to bow to. If it becomes super acceptable for candidates to walk out whenever they don't "feel" like it in the interview, if you can ask the employer intrusive questions about their professional lives to dig into the culture of the company, if the candidate has the resumes of their interviewers, maybe then there's more of a tit for tat in the interview.
But how many have you interviewed and not extended offers to? If that number is larger than the number you have extended offers to then that would indicate that developers does not have the upper hand.
At the very least for the last half year, I think developers may have an "upper hand".