Esper got the shaft in the "Sovereign" cycle, just like they got the shaft in the Ultimatum cycle. Prince of Thralls was bigger and comboriffic, Hellkite Overlord was the essence of TIMMAH, Godsire could attack and put out absurdly big tokens each and every turn, and Empyrial Archangel was absurdly hard to remove and did a great job protecting its controller. Compared to them, Sphinx Sovereign is rather "meh". But that was OK, because in Alara Reborn, Esper got cyborg Akroma.