Putting aside that your post kinda reads as if it were written ten years ago (most bootcamps do not teach Rails and it's vanishingly unlikely it'll reach the position it was ten years ago: cf JavaScript), I take some issue with
> beginners can use it without understanding too deeply...So there’s just going to be too many folks who will choose rails over more suitable languages.
It's not about "beginners" or "more suitable languages". You need an ability to build highly specialised software and you need general frameworks that will not be optimised for {specialised thing} but can do most of the things that you need for a certain task without having to hand write everything. Without the latter, all that happens is constant yak shaving and reinventions of the wheel. Rails (for example) is highly suitable for many things, getting clever points for not using it is great, but it's not very practical.
A lot of bootcamps in Europe are still teaching RoR. (I doubt "most", but I also doubt "most" for any single language once you include JS for front-end/"full stack", Java for "back end", and Python for ML/DS focus.)
Bootcamps sell themselves based on employment placement, not cool technology or deep knowledge. In this regard RoR, Java, and even PHP are going to be bootcamp milch cows for years to come.
> beginners can use it without understanding too deeply...So there’s just going to be too many folks who will choose rails over more suitable languages.
It's not about "beginners" or "more suitable languages". You need an ability to build highly specialised software and you need general frameworks that will not be optimised for {specialised thing} but can do most of the things that you need for a certain task without having to hand write everything. Without the latter, all that happens is constant yak shaving and reinventions of the wheel. Rails (for example) is highly suitable for many things, getting clever points for not using it is great, but it's not very practical.