It might be better to allow XYZ since it seems many of the decks here use them as well. If it helps this case any, I do remember that the GM of a different Yugioh RP banned the use of Number and Cxyz monsters. I personally didn't agree with prohibiting the use of the usual Number monsters since they aren't too bad (most of the time), but I don't think anyone minded their Cxyz counterparts being gone considering these ones are the crazy, pretty much broken cards.