After a few hours of testing, I found a few things out that occurred way too much to be coincidence, or occurred every time . All of this was done with a 61 Tyrant with oop prophet buffs and no other party members. Mobs are white name.
1) Auto attacking spawned more often than using skills. - Did 2 hours of just spamming Force Blaster and Force Storm on Crimson Drakes and Palibatis. Most of the time only spawned 1 or 2 Earth Guardians, but pretty rarely when using skills, compared to 3 most of the time and more often when auto attacking.(Could actually just be a stupid coincidence)
2) Having any other mob in the vicinity when a "Spawner" mob dies, decreases the amount of Earth Guardian Palibati that spawn. - Pulling 1 / 2 / 3 /4 / etc mobs at a time to test how many Earth Guardians spawned at a time. 1 Spawner should usually spawn 3 Earth Guardians. When i would pull 1 Spawner and at least one other mob (Including another Earth Guardian), I would never get a 3 spawn, usually just a 1 spawn and pretty rarely. (Please just tell me this was a luck thing)
At this point with the whole multiple mob thing, i feel like the way Earth Guardians spawn got patched but i wasn't able to find anything about it in any of the patch notes since i last played. Keep in mind, before i took a break, people were able to pull the entirety of the Seal of Shilen Doom Knight field and get the Earth Guardians to spawn "correctly".
Clarification would be appreciated, thanks.