The claim is pretty facially silly at a glance besides, though. You literally don't know the fields and methods, to say nothing of what they actually give you, on a Ruby object without opening either the code or pulling up Pry and doing `ls`. Which I have done, often enough, to fail rather stunningly to miss doing so when in Kotlin or when using TypeScript. Checked that one? Good news--now you get to drill down into the next one, and the next one. I hope that isn't coming from another library, too, 'cause jumping from library to library in Ruby or Python is a chore. And even if not? God help you if you're using ActiveRecord, I hope you enjoy scanning your database migrations or describing tables just to learn method names.
It is a bad scene. And don't get me wrong; I like Ruby quite a lot. But I won't make excuses for it.
Personally, with the actual tooling available to modern systems, I write TypeScript much, much faster--we're talking probably twice as fast--than I do even ES6, which I otherwise quite like. And TypeScript can't even assert whether something is a whole number or not, unlike better languages. It has replaced Ruby for me on the strength of that alone.
Vimal Kumaar touches on how it has helped them get employees contributing to the code a lot quicker, after they moved to PureScript https://www.youtube.com/watch?v=HLEwYghBjo8 (I think around 24+ minutes in, but I recommend the whole talk).