Wouldn't a LitRPG with an OP MC be a Superhero story?
To me they are.
Technically anything with a character who has "better than human" abilities could be considered a "superhero" story - from the legends of Hercules, to Superman in Action Comics. From the Saga of Beowulf to Twilight. From the tales of Gilgamesh to My Vampire System.
Even a lot of the pulp stories would be considered superhero stories, whether the character is truly superhuman like The Shadow or The Green Llama, or just "very impressive" like The Domino Lady, The Green Hornet, Zorro or The Tarantula (Master of Men).
Also some science fiction epics like the Skylark saga or the Lensmen novels of E. E. "Doc" Smith have superhuman characters (heck, some of the Lensmen could probably beat up Superman, and the Skylarks pretty much defined psionic abilities, though the Deryni novels may have explored them more thoroughly).
In many cases, a "superhero" story involves a character who conceals their identity and who fights other hidden or disguised enemies, and most of these characters have, at a minimum, a superhuman capacity to take damage (The Spirit, Batman), while some have truly impressive (Superman, Captain Marvel (Shazam), Captain Marvel (Mar-Vell), Captain Marvel (Monica), Captain Marvel (Carol), or Spider-man) or just plain bizarre (Plastic Man, The Creeper) abilities.
