An excellent question, my Texas friend.
Should you ever make it to Geno's, you'll be happy to know that you can order or cheesesteak made with American or Provolone, as well.
(Amazingly Cheez Wiz, though an abomination in or on all other things, works better than you'd think on a cheesesteak. Geno's is open 24 hours, so another key may be going there at 3 or 4 in the morning.)
Provolone it'll have to be, then, because despite the name, American cheese is not cheese. :)
But if you say that the Whiz is worth the taste, I will take your word for it when the opportunity arises, since you are clearly better-versed in the subject than I.
(Dammit, now I want a cheesesteak.)