The latter is in the global namespace (or you have to create a module/namespace for it). The former is encapsulated in a class. Encapsulation is nice.
I think a lot of these debates come down to repl development versus ide development. I’ve done a lot of both, but many complaints come down to people on one side not understanding the way the other side works.
No, it doesn't.
Pervasive OO style and monkey-patching core classes are orthogonal. Ruby favors the former strongly, and supports the latter, and Rails rather heavily leverages the latter (to the extent that it has been harshly criticized for it by much of the non-Rails Ruby community), but there is no necessary relationship between them.