I'm talking less exos/limiteds and more runes per faction, Last expac each faction had an average of 3 non-exo, non-limited/legendary champions. with a 1:1 ratio of them in most cases.
I'm pretty sure this is largely a carryover from SOE regarding rarity and factions involved although I may be mistaken and all that was already finished was the art. At any rate the balancing should be different.
I was under the assumption as well that the ronin were a carry-over Legendary release. A full expansion would be great but that is probably far off.