I've worked with Ruby for over fifteen years off and on and the last seven exclusively -- in a large codebase with a fair amount of metaprogramming. We've onboarded engineers, junior and senior, who previously have never used Ruby and it's been interesting to see who does and doesn't have a hard time with it. It doesn't seem to match overall experience and skill level. It's more of a sense that people with patience and a kind outcome oriented approach (over fixating on why something is done a certain way) will have an easier time unwinding the complexity.

One thing I've noticed, and this is something that seems to bother non-Ruby engineers, is the people that flourish in a complex Ruby application prefer to read code over documentation.