Well, as someone who has taught different languages as first, second and third languages to students and young pupils I would say it becomes easier. Not easy in an absolute sense. It still requires effort.
I would however agree with you that those who say "it's easy to learn another" in an absolute way has usually only considered languages from the same group so far.
I would however agree with you that those who say "it's easy to learn another" in an absolute way has usually only considered languages from the same group so far.