John started casting Summon the Eastern Lord after finishing summoning the mighty ape. The summoning spells of the Western and Eastern Lords had intricate runes in their spell formations, so it took him some time to complete the summoning. The time needed to cast these two spells was worth it, though. Once the mighty ape and the mutated saurian emerged, he could pretty much leave the fight to those two.
However, he didn't do so. He continued casting and summoning his other minions. They were the avatar incarnation, giant lizard, dirt golems, Fae, Armored Feral Tiger, and Water Elemental. Together with Steve, these summons formed a perimeter around John, Purple Mist, and Trinity Dawn.
John's Monster Overlord had a similar passive ability to Badass' Hell Ruler. All their summons were immune to being controlled or dispelled. Additionally, his Avatar Incarnation no longer had a duration. Its cooldown only began when the avatar was destroyed.
