It can be deemed as a "massive positive" for RoR only when "slow dynamic bytecode-interpreted globally VM-locked language running a massive completely-overkill framework" is a good thing.
Developer efficiency is notoriously difficult to measure and prone to all sorts of biases. Perhaps the key word in your sentence is "I"?
I've done my fair share of both Java and Ruby web development, and without a doubt, I was much faster writing Ruby.
For non-trivial Java apps, startup time was > 20 seconds. That kind of REPL while developing kills productivity and developer satisfaction.
The last Java app I wrote had more lines of configuration than my first Rails app had lines of code, at equivalent complexity.
The first Java job I had required a full-time script writer, a DBA, and someone to keep the web server up. In Rails, that entire team would have been shrunk by 75% (mind you it didn't exist back then).
I do work in other languages. For machine learning, Ruby's speed is a killer except for toy data sets, so I have used Octave and Python. When it comes to the web though, Rails really did do many things right, from a sane MVC, default ORM, helpers and migrations. There are times execution speed trumps development speed. For fast dev on web apps, Rails really was cutting edge and for those with an investment it can still be a better trade-off than doing something in Go.
It still seems as though these frameworks are all playing catch-up, with e.g. things like migrations.
The only way to reach 6x is with 3rd party libs you have in RoR but you have no equivalent on say the JVM. Massive code reuse is the only major productivity gain today.
[edit] Sorry my mistake. If 50% of your time is taken by other tasks when writing say Java code, the most you can achieve is doubling your productivity by reducing development time to zero. If you tripple your productivity during development, your overall gain is 33% I think (not that good with on the fly calculation obviously).
[edit2] Just realized, this is Amdahl's law for developer productivity with your other tasks being the sequential fraction.
Of note, many of the best Ruby / Rails folks I know moved on to much better roles, whether CTO at growing companies or started working on cash-generating projects. Once they optimized dev time, they got more time to work on things like design or copywriting, and optimized the hell out of that too.