Notably, Stripe does not use Ruby on Rails: instead there’s a few homegrown frameworks used for routing, storing data in a database, etc.
I think all the big shops have most senior ruby devs locked up. If one has any meaningful rails and ruby experience under their belt they can stick their thumb out and land a job immediately.
We would prefer to hire talented ruby devs, but they just aren't there.
The contributions of a senior ruby engineer in a large, complex rails codebase will be immediate and will have a long tail over someone that has no experience in rails or ruby. This seems self-evident to me. It's just that there aren't enough of them.
It takes like 1 month to ramp on ruby, maybe even less. The cost of one month of ramp is highly justifiable given the fact that it's hard to find anyone who knows ruby (for real knows ruby) & most of the ramp is on system specifics anyways