The vex and let me tell you why because there are vex that can rewrite time such as gorgons but they are most likely not even that strong atheon is basically a manager at a vex store on Venus obviously the vex don't originate on Venus hell they probably have even stronger vex on mercury or any other planet they been to and mars they keep the cabal buisy on the surface while seeding the planet like the hive did to the moon and eventually the hive and vex will fight over earth and the moon there are are vex that came before and after atheon there are vex who pray in the black garden to something immensely powerful why else would a super smart race pray at all there are vex all around the universe and they can teleport and a moments instance across the galaxy they could've sent more vex to save atheon but they determined he wasn't worth it because there are vex leading the show they are real leaders and most likely your spartan with a magnum or sayian would get shit on by the leader of the vex