My own experience at ChartMogul with building production services in Ruby, Go and Rust is that the overall throughput of REST API type services increases a disappointing amount.
With JRuby you get to retain all the benefits of the Rails ecosystem. Most of the Go and Scala community is driven by much larger companies who do open source libraries but they don't really build frameworks to help developers build software quickly.
Rails performance relative to JVM+Scala+Play is tricky to measure but the closest thing to a decent benchmark I know of is this: https://www.techempower.com/benchmarks/#section=data-r16&hw=...
My own experience at ChartMogul with building production services in Ruby, Go and Rust is that the overall throughput of REST API type services increases a disappointing amount.
With JRuby you get to retain all the benefits of the Rails ecosystem. Most of the Go and Scala community is driven by much larger companies who do open source libraries but they don't really build frameworks to help developers build software quickly.