What demon summoning are you talking about? If in the final battle, instead of attacking, the demon's troops stand still on their first turn, it's a guaranteed loss. The strength of Inferno lies in the initial strike of Nightmares + Dogs, now with Jumpers, then you can summon Pits from the Death Knights if you have Devils. And all this gating is nonsense in the final battle; the main troops will simply fall faster. The only exception is the gate of Imps to drain mana again.