The way I see it, the summoners are really evokers or conjurers (not in the XIV sense, but in the general sense) that form the egi creatures from aether with the same aspect and flavor as the actual primal. From what I gather, the egi are created from a very tiny fragment of the actual primal's power and built up around that with aether.

For scholar it's a bit different, as Eos and Selene are actual independent entities rather than poorly-made and vastly depowered copies of the original.