Carbuncles are classically DPS aetherial construct from Arcanist lore, not shield/healers. Yet SMN carbuncle can casts Radiant Aegis and SCH can glam Eos → Carbuncle making it a healer.
Also, since summons apparences depends on the aether of the caster, it would make sense that players who main SMN/SCH have access to fairies legally in-lore. This glamour would just be a cosmetic nod to multi-job life.

(Let us have machine-gun Eos please :') )