Hmm I can imagine that while LLMs are good at producing working code in Go they might not be as good at structuring larger applications, compared to building on opinionated frameworks.

I imagine there could be some presets out there that guide the vibe-coding engines to produce a particular structure in other languages for better results.

Is that specific to using Rails or it is good with plain Ruby as well?

Rails, I haven't tried at all with plain ruby, but I doubt. I think formulaic = static typing for AI