Obviously Nasus could probably wither the flesh from most of them, and Xerath could blast them with arcane magics into powder, and none of them could put up a fight against Aurelion Sol.
Against other "immortal" champions, though, I think people underestimate the mortals. Xin was slated to fight 300 men in the fleshpits. Each won fight means more fighters added. They didn't make him fight 20 men and then jump to 300 to see him die. He can handle as many men as can stand within killing range. He performs as well as a lower-case g god when weapons are in play. Aatrox may be a god of war, winning every battle he fights in, but Darius also wins every battle he is in. Darius' stalemate vs. the Winter's Claw, who fought Olaf to a standstill, who killed a giant monster in a frenzy. All of these champions are inhumane on the battlefield.
Kayne has withstood the corrupting power of a Darkin through powerful will. As a child, he killed many grown men. 60% more mass as an adult, add in some actual training and OP shadow powers, and why couldn't he escape a 1v1 with Renekton alive?
Do I think Talon or Twisted Fate could kill Cho'Gath or Azir? Obviously not. But I think in a battle against "gods," as long as there is no continent destroying magic in play, they could handle themselves better than a lot of people think they could.