> insane P/E ratios became the norm and maintaining them is harder when you’re raising salaries

P/E is the inverse of earnings yield. It varies with rates. So 2% -> 1% equity yield means a doubling of P/E. But framed as a yield shift it looks less dramatic (and more familiar).

How do large P/E ratios impact salaries?

I don't think this would pass much scrutiny, but I suppose you could have a situation where a small number of people that own a large number of shares in a variety of companies could become a monopolistic unified force that could put downward wage pressures on entire industries.