You're missing the part where more often than not it takes multiple runs of a Ks99 to get one BB item.
You also get pop items for the regular NMs which means more chances to get the items. Black belt is stil basically THE most powerful non-weapon item for MNK. It SHOULD take some time to get. That said, if you take a group to do KS99s and at least a few of them bring an orb, you're probably going to get your item.It's not like crests/bst seals/k crests/k seals are that hard to get. Get some friends to come that don't want 'em and pool them to you.