There's a big difference between a senior who happens not to have worked on a particular tech stack in recent years and a junior that happens to have got starte

There's a big difference between a senior who happens not to have worked on a particular tech stack in recent years and a junior that happens to have got started with that stack. The senior will definitely be able to command a significantly higher salary and within a fairly short period (months if not weeks) should be able to demonstrate that value. There's value in knowing a particular stack inside out for sure, but it doesn't match the general skills and experience you can only gain by having worked as a developer over a decade or so.