why Argüelles thinks it's possible "for an average Joe", i.e. not for a literary scholar but just I random person who's an avid reader and would love to read great books in the original.
I don't think is even a debate if is possible or not. People already did that, some surpassed that number by quite a lot. So, maybe a better question would be : is it probable? And now we come to another question, how much time and effort that "average Joe" is willing to invest in that endeavor? A motivated "average Joe", with enough stamina and discipline would succeed most likely. Could be a post factum debate if Joe is still average or not after that feat, but there is no reason to think is impossible.
People fail more often by lack of trust in own skills, discipline, motivation and such than by lack of capabilities per se. As a fun exercise, imagine a benevolent patron would grant you one million dollars for each language you bring to that level (minimum 6). Pretty sure would give at least a good try at that. So "average Joe", avid reader that would love to read great books in the original, has to check his motivation against that example.