I think that this issue of what makes things timeless is a lot more complicated than is really being grasped here.

When I started university I quickly learned that all high culture is (such as the works by Kafka and Hemmingway etc, along with things like classical music and art) are in many ways, just aspects of culture that have been adopted by the upper middle classes.

The way upper middle classes talk about Fitzgerald, Rodin or Wagner, are no different than the ways others talk about more 'low-brow' works of art and media. It's just that adoption by the upper middle classes come with a veneer of legitimacy that allow it to bleed into other works and become a building block of culture itself (a reference to the green light across the bay will get you quite the chuckle at the right dinner party- a reference to the Shire? not going to fair quite so well).

Does that mean Fitzgerald is shit? Of course not. Art and artists that have the legitimacy of the middle classes is very well curated; but just because something didn't get that legitimacy for whatever reason doesn't mean it couldn't be timeless. The reason we've heard of Fitzgerald, Hemmingway and Orwell isn't only because their work is the best of the best (although it is some of the best I've ever read), it's because the right people decided it was acceptable, and so they became a part of 'culture' rather than media.

Of course the person you're responding to has drunk the cool aid and decided that anything aiming further than it's own narrative is elitist- the problem is that we have this false dichotomy between the two camps. On the one hand: 'Literature' is poncy elitist crap for the coffee table whilst genre fiction is the bees knees where quality writers tell quality stories. On the other hand: Pah! Kafka is timeless! Hemmingway is timeless! all sales mean is that enough plebs have decided to buy it like sheep! Look at 50 shades!

I think the truth definitely lies somewhere between the two. Classics are classics for a reason, but a large part of that reason is because the right people liked them.