It's really simple. The beasts you summoned did the bulk of your damage. Not a measly 33% nor was it a glorified DoT. And you could Summon monsters in other titles to do said damage every turn. MP resources were fine. To the point a BLM's high tier spell was comparable to high level summoning. Along with defensive summons that bolstered your defense like the Golem's Earthen Ward from FF5.
Furthermore in the older games Summons were acquired upon their defeat and not in job quests. And since this game has set the mark for Summons are bad and you shouldn't do it, it just cements the fact that true Summoners have no place in Eorzea.
