Sending a message to an Erlang / Elixir process to change its internal status (a GenServer) is not conceptually different than calling a method of an object.

The big difference I see between Elixir and (example) Java or Ruby is that everything is an object in those languages but a big Elixir application has only a few GenServers, where keeping a state matters. Everything else is passed as argument, which by the way it's what a GenServer does internally with an endless tail recursion.