I, as a developer reading your code 6 months later, care.
When something fails, it's nearly impossible which of the magic methods were injected by which magic library.
pry> show-source SomeClass.class_method
pry> show-source AnotherClass#instance_method
# List an arbitrary object's class methods, instance methods, methods mixed in by included modules
pry> cd some_object
pry> ls
there's heaps of good tooling for finding the
method source and docs dynamically
If I have to run code just to see where `Foo.bar` is defined, that makes things... about an order of magnitude harder to understand. I mean, that's really tough thing to do in anything but a trivial codebase.
This is nearly 100% the fault of developers, not the language itself, but I would suspect that most Ruby developers spend a significant amount of time dealing with things like this because it's how the ecosystem rolls.
Determining which method responds to which message is only possible in an instantiated runtime, but that’s true for any late-binding programming environment. Complaining about it tells us more about the complainer than about the language.
If you're writing a library doing things like this is a bad idea (except in very limited circumstances). And to what seems to be every non-Rubyist's surprise, virtually no libraries in practice actually do this sort of thing so there are never problems in practice.
The times I do this sort of thing in my own application code, I put the methods in a module and have a hook that raises an exception if the methods already exist when the module is included. This is the best of both worlds: I can add features that don't exist, but am informed immediately when my app launches if such a method has already been defined.