What demon summoning are you talking about? If, in the final battle, the demon's troops, instead of attacking on the first turn, just stand still, it's a guaranteed loss. The strength of Inferno lies in the initial strike of Nightmares + Dogs, now with Jumpers added, and then Pitfiends can be summoned from the Dead, if Devils are available. All this gating is useless in the final battle; the main troops will simply fall faster. The only exception is the gate of Imps to drain mana again.