Recently online theres been a lot of sturm und drang about a category of books that don't really have a particularly strict criteria but generally are lauded by a subset of literary cliques on twitter and usually published by New York Review Books, Dalkey Archive Press, or Deep Vellum or maybe Archipelago Press. These books can be long, short, translated, untranslated (in the anglophone context), Modernist, Post-Modernist, usually male authors but not universally so, the only criteria about the works themselves is they're capital L literary, in the difficult and dense way. For specific examples I'll quote from the Los Angeles Review of Books article (Against High Brodernism) that caused the most recent flare-up of micro-discourse :
William Gaddis’s The Recognitions (1955), Mircea Cărtărescu’s Solenoid (2015), William H. Gass’s The Tunnel (1995), Péter Nádas’s Parallel Stories (2005), Thomas Bernhard’s The Loser (1983), Thomas Pynchon’s Gravity’s Rainbow (1973), Vladimir Sorokin’s Blue Lard (1999), Louis-Ferdinand Céline’s Journey to the End of the Night (1932), Joseph McElroy’s Women and Men (1987), Michael Lentz’s Schattenfroh (out later this year), Miquel de Palol’s The Troiacord (2001), Jon Fosse’s works, Gerald Murnane’s The Plains (1982), Robert Musil’s The Man Without Qualities (1930–43), Mark de Silva’s The Logos (2022), David Markson’s (1988), Agustín Fernández Mallo’s (2006–09), and Hugh Kenner’s (1971).

Interesting... sounds like a similar phenomenon to Russell's History of Western Philosophy but in the literary context. Especially with the catty sniping and lack of rigor. My general distaste for this conflict of pretentious vs pulp lit is that it's a contest for who is more self aware; it's a question about the personality of the book's average reader and not the book itself. You 'win' the conflict by being a part of the self aware cadre who knows either that the other cadre is too plebian to engage with real literature or that they are too obsessed with looking smart to engage with honest literature; a book is good or bad only categorically. I'm not sure it's an immemorial argument as you say, it does seem to me peculiar to the last 100 years or so. I didn't know about the Ulster cycle, but you might have put me on to it...