Unless they add an elemental wheel there is no point to adding new Egis since we will use the one with the strongest damage. In this game Summoners harness and channel the energy of the primals shape it into a biddable avatar that's how we get the egis. Bahamut stacks/Dreadwyrm Trance allow Summoners to channel the power of Bahumat which is in line with what Summoner's are suppose to do in this game. If SE allowed us to channel the power of the other 7 primals and do a primal trance with them it'll complete my vision of what a Final Fantasy Summoner looks like in an MMORPG.