I think the issue with Rails, as a long time developer in that ecosystem, is that much of the default assumptions are a) not common (not so far off-piste that a human can't get used to them, but outside the center of the bell curve), and b) not explicit. So it's very common to do things like install a plugin that has across-the-repo effects but that is only documented in e.g. the config directory and the bundle. Unlike, say, NPM, when you install a new package where you explicitly have to e.g. import it everywhere you want to use it.

As time has gone on Rails has gotten better about this, but it still means that "your rails" and "my rails" are different enough that AI could easily get confused.

As you say, the other aspect is the intense dynamism which works against AI, which again prefers to have everything explicit and reasonable about from the text.

So I ended up going back to Javascript after a brief 12 year digression into Ruby. I still love Ruby but it's just not the right language for the current environment and team structures - typescript is "worse is better" in the right ways that it's a much better choice for both frontend/backend being the same and better type systems.