I don't know what build you're playing, but that reason seems weak. Why? Because the only creature that should worry about mongoose is kird ape, and that's what, 4 cards in your deck? (Maybe you play Isamaru, but you shouldn't because it's not good enough.) Rancor is not really needed for goyf either, because you have burn. Which, by itself rarely kills goyf, it makes goyf trades go in your favor.

Also, how does "If you allow yourself to get 2 for 1'd then that was your player error" make sense for reasing? It seems to me that rancor should be an aggroish card, you want to put it on your creatures, right? But now...If you fear removal and don't play it, then it's not doing you any good at all. And if they had removal, wouldn't you just want a creature (to replace the one that was removed), or some other good spell you could actually play?

Rancor can be good, but I feel that you have to jump through too many hoops to actually make it worthwhile, and at the same time I don't feel that it speeds the deck up more/enough/at all over another creature or some good spell instead.