There are compensation consultants that many companies use to benchmark salaries. The same thing happened at my company, salaries went up quickly so they adjusted everyone. Before that new hires were getting higher salaries than people with more experience who had been there many years.
The rate required to stop experienced developers from leaving. That's quite easy to measure. Enough of the people will leave will tell you what offer they got, and you adjust up until the rate of turnover is acceptably low.
From my experience, there's always a company willing to pay you more. If they see some company paying you X, they think your skills are worth at least X.
So your explanation doesn't really answer the question.
