Rails “convention over configuration” approach is probably also more LLM friendly. Convention can be trained into the model itself, whereas configuration takes up precious context.

I have definitely found this. A few months ago I tested Claude coding a web task in Rails vs Flask. Claude did much better with Rails - I think the opinionated Rails conventions helped the AI. However, Claude didn't complete the ask in Rails. A couple of weeks ago I revisited a similar task with one of the latest AIs. It sailed through it in Rails (didn't try Flask).