I was not around for the first three months of Mist of Pandaria, but I have heard that this was possible at first when it launched. This is the sort of thing that is tough to find in Beta Testing because who, of the thousands of testers, would sit and do that over and over in beta when there is new content to play with. With retail release after a few months millions of people are done with content and find these sorts of things. It was changed in a patch early on in that expansion. (again just what I heard, I have no first hand knowledge)
I think a similar thing is about to happen to the menagerie pet battles, tons of exp can be made from repeating the right battles over and over. Reports from Test Realm are that the exp is seriously nerfed.
- Morlis Alliance Kael'Thus 100 Shadow Priest (main account)
- Morlïs Horde Madoran 100 Beast Master Hunter (main account)
- Vandì Horde Madoran 100 Arcane Mage (alt account)
- Lots more alts though not near what Doob has... haha