Earlier quoted context omitted.
Could you elaborate more? Your comment doesn't make much sense otherwise - if anything I'd argue that NOT tying yourself to a single framework is what makes you grow into a senior developer. I'd argue that Python (or similar) back-end and JS-flavor front-end is a better path to growing since it's just a much wider area of growth.
Updated my original comment to include my story. Once learning Ruby/RoR techstack, you can jump to all other techstack in NO time as it already taught you everything you need. The rest is ecosystem and syntax. About your concern, other frameworks/languages offer you only part of story, Ruby and RoR offers you complete story in a concise way, it's the difference.
Most systems use similar-enough patterns you can carry them over where-ever. It doesn’t have to be rails, but it was for you.