I partly agree with what you're saying but still - you're exaggerating. Doing Rails without a decent knowledge in Ruby is exactly what you said - it's being a junior. You'll rely on the existing codebase without any ability to provide your own ideas, only shifting code from here to there without fully understanding what you're doing and will always need a senior whenever things go awry. That's what being a junior is like in any language.
I don't think we can compare languages based solely on the experience of juniors. I'm not saying it's irrelevant, it is, but it's only a part of what writing software is. In the end of the day you need the seniors and people who really get it to maintain the code and steer the ship in the right direction.
But I do agree that Rails is a kind of dialect of Ruby and that you can get pretty far with Rails without being great in Ruby (you still need to be decent though, no way of getting around that).
> Most Rails programmers I've worked with live in the controller and the view
Where is the business logic at? They also write services or something similar or stick it in the Model. Whatever isn't ActiveRecord will be pure Ruby - Rails has no opinions there.