The new gate spell adds some summons that offer a lot of flare and flavor. I love alignment themed summons, they add a lot too adventures and encounters. Holding back the forces of Baator with a Balor or Deva is such a cool concept.
The current problem right now is you have hardly any time to RP with your summons before they wander off. If they were designed to fill the niche of "short duration but big help" I think black blade of disaster trumps them there. And as far as balancing goes, I think it will be fine, considering warlocks have unlimited supply (no spell components or piety required) of balors with much longer durations.
Increase Gate Duration
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