I'm in a similar boat to you - I've built non-trivial side projects in other tech stacks, but I'm a JVM developer at heart. I've been conflicted about whether to dig into ruby/rails more to jump ship recently because of the philosophy in the community.

I love kotlin as a language and enjoy working with spring boot but the hype in the JVM community around JSON API + React SPA does make me wonder whether I'm moving away from it philosophically.

I'm particularly excited by Spring Native right now. Having a Spring Boot app startup quickly and use less memory will fit heroku-like PaaS environments perfectly.