My experience has been the opposite with Rails because of open-ended patterns with Hotwire. Sure, Rails itself is opinionated but Hotwire provides multiple ways to do the same thing, which confuses LLMs. For example, recently I tried building a form that allows creating related objects inline using modals. Claude 4 Sonnet got quite confused by that request, no matter how much help I provided. It managed in the end but the solution left a lot to be desired for. It can build the same feature using React on it's own with basic instructions.
Same thing with other libraries like HTMX. Using TypeScript with React, and opinionated tools like Tanstack Query helps LLMs be way more productive because it can fix errors quickly by looking at type annotations, and using common patterns to build out user interactions.
I find Claude works extremely well at generating Stimulus controller code. Likely a lack of documentation and git repos with larger Hotwire codebase patterns that it was trained on.