If you watch the last trailer you see a scene were Varicks confronts Erimis about using stasis and how its changing her.
My thought is, she likely knows we defeated oryx who was basically the cause of the fallen whirlwind event. So she could probably guess that guardians are strong enough to defeat her even wielding the darkness. So what if this is a set up similar to say Captain America: Civil War. In which the villain turns the heroes against each other and forces them to fight each other, essentially doing what no other villain has done before.
If we learn stasis and become corrupted we could turn on each other, similar to the kentark team from GOS raid. Taking a step further, this could also be the pyramid ships plan and the reason it gifted its power to Erimis. By corrupting guardians, it could cause the traveler to leave as was mentioned in an old piece of lore which speculated that the traveler left its previous hosts when they became corrupted and sinned against the traveler
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1.(Theory)The Fallen Whirlwind was like our Collapse, and Oryx, no matter how Powerful he was, couldn't cause that Type of Calamity(Yes he committed Genocide on countless other World's).Oryx got to the Fallen like just After the Traveler and Pyrimid ships left. 2.The Collapse or Whirlwind in Record was only ever caused by the Pyrimid ships or The Darkness. *Now, It's in Theory That Oryx caused their Whirlwind, but it's also Possible at Account 1. The Fallen themselves of what I found, don't even know who caused thier Collapse. As it happened like a thief in the Night. 3.Yes Oryx followed the Traveler, but he never got close enough, always missing it. That's why Crota was on the Moon, he Finally found it and got killed before he could launch an Assault. 4.Yes I believe Eramis knows that we Defeated Oryx, who doesn't? Any way... Ya. 5. It's hard to understand these types of lore, when there opened up to Speculation. Never giving an Exact Answer. 6.(Logic) it'd make more sense if * was True, why then waste your Time with Fallen if the Traveler was literally that close? 7.(Most Possible Outcome) In the Lore, after thier Whirlwind, after sometime, Hive ships then began to Drop down. It is possible that At Account 1 Oryx got there to late and Decided to commit more Genocide as the Worms need Death to Survive. Anything is possible I guess 🤷