I built my startup in Rails. I eventually re-wrote the entire application in Go as a monolith. In my experience, Go is just as productive if not more productive due to fewer errors at runtime. My day to day life is a lot better with Go-- no more exception emails, firefighting, etc.

I really liked Rails and used it for several years, but Go came when Rails was making things difficult.. Ruby's heap memory kept growing and not being released or released too slowly. My server was using 12 GB of RAM and could hardly handle 300 concurrent users.

The Go version uses 25 MB of RAM and can handle many thousands of concurrent users.

edit:

I understand the memory/concurrency issues are not Rails' fault entirely. It's likely ActiveRecord and Ruby as a VM that caused most issues, but it's part of the Rails deal. Getting good concurrency with Rails isn't easy, and memory issues are real.