How recent were your experiences with this? In recent years I've seen monkeypatching treated as more of an antipattern. If you are on a project where people are doing that without very good reasons, that says more about the team than the language.
It is still prevalent enough that when developing Ruby JITs it can be worthwhile delaying compilation until the framework has started up and finished invalidating all your method lookups, or changing your invalidation strategy to handle new methods being defined on Object without invalidating all your inline caches.
