Yoshi-P was clear when he said only Arcanist will have access to Carbuncle and that Carby will have several uses , as example he mentioned Carbuncle Tank and Carbuncle Healer so in a few words Carbuncle will be FFXIV's Eve from Pokemon.

SMN will be a pet class but Yoshi-P is aiming for the old school SMN that called Primal for a 1 hit move then leaves
except this time we will do it with Primal's essence they might look like aether/ghostly forms of them not full body.