A lot of event units aren't worth using purely because premium units rule the roost, as they should.

The advantage of not having any premium units though is actually putting to use all the maxed out event/TP units you acquire as full-time members, and not 100% trivializing events through an above curve premium black unit.

I recognize that it's not for everyone, though. I certainly have a few premium units I wish I could have, and I'm a bit of a liar since I rerolled until I got a black for my first summon (got Deine then never rolled again, and she has devastated plenty of bosses for me).