In the Song of Roland, Roland and his allies make a last stand at Roncesvalles against an army of ~30-50,000 paynim, and slaughter 10,000 of them before finally being overwhelmed.
In one of the climactic battle scenes of the recent wuxia film _Hero_ (
www.herothemovie.com), two uber-badass swordspersons storm the Qin Emperor's palace, which is garrisoned by 3,000 elite guards. The guards are cut down like chaff before a scythe.
Heck, even in the relatively low-powered LotR movies, there are plenty of scenes of heroes taking on armies. In FotR Aragorn single-handedly takes on a battalion of orcs and slaughters stacks of them. In TtT, Gimli and Aragorn take on more orcs at the gates to Helm's Deep.
Huge battles featuring ultra-powerful characters wading through armies of mooks are a staple of myth and legend, if not modern fantasy. It's one of my dreams as a DM to eventually run a fight pitting thousands of orcs against a group of 20th level PCs. I'm not expecting the orcs to win. It's all about extravagance.