A modern rails setup with system/user level isolation usually requires homebrew and rvm or similar which is quite involving. Compare that with install java, hit new play app in IDE (or download template) and just run, and I'd say Java has a pretty good recipe for productivity. Deployment? Just copy a fat jar created automatucally by the build system and java -jar it, no virtualenvs in sight.
So would I pick Java for a business? I don't know - I personally enjoy programming in Python way more than Java and would probably go with it, eventually regretting it...
It's just a different set of skills to pick up, no different from any others.
My current go to for quickly starting projects is spring-boot, jooq, and postgres.
And the basic jvm settings will get someone a long ways - much farther than an out of the box Rails setup.
But when it all goes tits-up it is a lot harder to work out why.
Also, I'd forgotten just how much i hated annotations. And now I need eye bleach :/
I like spark because it maps very closely to Sinatra in ruby, and doesn't require much additional support.
How so? Maybe you're just more comfortable with a different environment?
Of course Go and Ruby work out of the box. On the other hand, their runtimes are kind of lightweight and less general purpose as the JVM.
To many people this is somewhat akin to black magic. CMS, G1, PermGen, Xmx, NewRatio... it takes time to get to grips with even the rudiments of the JVM, and many places simply do not have the expertise.
Also, it takes time to set up a JVM stack. You can have a rudimentary rails app running in a few minutes; it took me several hours to get a lightweight spark / mysql PoC up and running.
Java is performant, but it falls down in terms of RAD when contrasted against languages like Go and Ruby and against frameworks like Elixir or Rails.