Most good engineers(especially early in their career) will be an order of magnitude more productive after a couple years at the same company, as they build up both domain knowledge in their tech space, and institutional knowledge that can't be learned outside of the company. And companies know the value of this experience. That's why you can switch jobs after 2 years for a 20-40% increase. When the market rate for your labor is 1.2x your current salary, I think that's called underpaid.