Yeah, duh, that's why we hire devs with any talent -- like I said. I'm not sure what you are pushing back against?

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.

I'm pushing back because I've had the opposite experience. I've started in a new team with exceptionally talented people, all of whom who have never written a line of ruby, all providing incredible contributions and hitting all our (pretty crazy) dates. All in a large highly complex ruby monolith.

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