I don't agree with this sentiment. There's something to be said for competition, closeness to hustle and bustle of an industry, and the sheer learning-by-osmosis that happens in an area densely populated by a certain industry. As much as I think that senior devs are needed in the industry (I've been in startups without the proper amount of them and it's terrible), there is a lot to be said for the benefits of being a young developer embedded in an industry hotspot.
I've never lived in SV, nor do I want to -- there are areas of the US that pay SV prices with lower cost of living and progressive citizenship/policies, which I'd rather not name since then whoever's reading this would move there -- but the assumption that a "senior" dev in a low cost area is more valuable than a "beginner" dev in a high-cost area like the valley rests on a bunch of things that often are untrue/shaky at best.
- How do you even determine senior vs. beginner? Years of experience? Successful projects? Breadth of technology knowledge? depth of technology knowledge? interaction/propensity to share knowledge with team members?
- What has this senior dev in low-cost area been exposed to? What about the junior developer? If I asked them to solve a problem, which can imagine the widest breadth of possibilities? which can imagine the most stable/future-proof possibilities? This can come down to the person almost as much as the years of experience.
- What frameworks/tools/language are you talking about? (this seems like it may not matter, but if you're measuring contributions to a codebase, a developer with 1-2 years of experience in purely golang is going to be better/likely faster at grunt work maintaining an API in golang where the design choices have mostly already been made). Higher level refactorings and architectural work will likely be out of their reach for months/years to come as they mature, but if what you really needed was someone to put out fires with code that isn't terrible, 1-2 years will often suffice. It wouldn't take the senior engineer very long at all to learn the new language but they'll also have to spend some time unlearning old habits -- of course they'll also be bringing good habits that you may not already have as well, but happily dealing with grunt work and over-working yourself because you're "super psyched" is usually not something senior engineers will do -- newcomers/greenhorn often do this, however.