Not sure about Ruby in general, but Rails is an excellent candidate for LLM assistance. It’s very much convention over configuration, been around since forever and there isn’t a question somebody hasn’t already asked on Stack Overflow.
This is the thing when people say "LLMs write the boilerplate code for you"--why are you writing all that boilerplate? If you're dutifully cranking out boilerplate instead of creating abstractions that make it unnecessary to write boilerplate, you're a mediocre engineer at best. Add an LLM, and now you're a mediocre engineer with a mediocre simulation of a mediocre engineer.
Aren’t most business apps almost exclusively glorified CRUD? Like the sort of CRUD stuff Rails is amazing at. Those are basically all boilerplate, it’s more of a question of which flavor of boilerplate you need for a given use case.