Erm... quantity vs quality.
If theres only one minion, it should be of better quality.
If theres many minions, they should be of lower quality.
That's two styles, not three. Unless the benefit of only one minion is NOT having higher quality. Which would make no sense...
Possibilities for Summoner type classes include:
Sentry specialized summon class (as added in the last update with the Old Ones Army) which increases sentry number and possibly increases the power of the original sentry summons (queen spider, frost hydra) in exchange for having a minion count of zero.
A minion debuff type class. Basically, level ups grant the minions themselves additional properties such as inflicting debuffs on enemies. This would be more of a utility class that has the minions weaken the foes so that the player can fight them more easily. For balance sake, the minions can havereduced damage but increased knockback, further exemplifying their support theme.
A Magic Familiar, Spirit Animal, Caretaker-type class would be quite good. Basically, the summons get stronger than usual, but not too much. On the other hand you are limited to only one minion of each TYPE, though the overall limit of minions also increases by level. Basically, the player will have stronger minions, but will have to use a variety of minions instead of a ton of the same minion. Might even get a boost if the player has a pet/light pet equipped.
Btw- cool idea with the hybrid class being able to branch out!