I think it's his mimicry, he can tap powers from more than just mutants and at vast distances, the Omega part is probably how many powers he can store in muscle memory to not require synching for example being able to use any power repeatedly even if he copied it once and accumulating every power on earth over time becoming like Josef Huber in a sense (if his power evolves to that point anyway). That's about it. I use the same reasoning to despute that he is 'Omega' for channelling Omegas for the simple reason that Fabian Cortez although he can boost many mutants may not be able to boost Omegas because they have no power ceiling to boost to, in effect he is boosting to infinity .With that logic too while Synch can siphon an Omega very well , he cannot siphon the full potential to imitate any said Omega like for like ,clued in by his tapping out after siphoning Jean