Lorewise, I'm sure we could figure out a way for Summoners to control weaker Primals for one special attack that uses all their aether, then they dissipate. I don't think summons should be permanent pets at all. They've always been one-shot spells until FFX/XIII had them out for a limited amount of time, then FFXI had them persistent but at least they were true summons and not egis.

SMN should be the only job that can make bigger explosions than BLM, but right now it kind of falls short. It's an awkward DoT class. Very questionable choice by SE.