This post will refer to the end of Shadowbringers 5.0, and it's something I've been thinking about lately and would love to hear your thoughts on the matter

So at the end of Shadowbringers, when Emet-Selch is dead and the First is saved from the light, we see a scene in which Zenos kills Varis, which stops the production of Black Rose. This poses the question however: Was the action of Zenos directly tied to our actions on the First? I ask this because if Zenos were going to kill Varis regardless, then there would never have been Black Rose, and there never would have been a reason for Graha to go back to the past to begin with. On the other hand, us going to the first implies that Black Rose did indeed spread in Graha's timeline, but how? Did Zenos not kill Varis then, and if so why not? Or is there some sort of higher power "fate" type of thing which made it so that our action in killing Emet-Selch lead Zenos to killing Varis - fulfilling his part on the Source and destroying both sources of the calamity.
What adds credibility to this latter possibility is the fact that Zenos killed Varis immediately after we killed Emet-Selch.

Time travel is always confusing and leads to potential plot holes/confusing stories, but I would like to hear your thoughts on this matter nonetheless.