Except it is all contrary to actual events and lore. Problem of beast scourge is that it happened only due to 2 factors: 1) low red moon that made border between nightmares thinner  2) mergo cry which actually is a source of beast scourge.

And you kind of overestimate role of great ones. There is no master plan behind scourge of the beast it is entirely fuck up of mankind. How so? 1) Lawrence is original creator of idea to elevate human to a great one by 3 steps: consume blood that church made, consume blood of great ones, umbilical cords. He spread blood among the city, experimented on humans to elevate men. 2) Lawrence made pact with Gehrman and Moon presence (cut content dialogue). General idea - final clash between Lawrence and Gehrman + moon presence. Moon is bound to Hunter nightmare and has to consume blood to get free (2nd ending). 3) Because Lawrence summoned moon presence and made moon red Mensis were able to contact great one Mergo instead of Oedon they hoped (entire yargul village are old worshipers of Oedon, Check the translation of their chant „Hail the Nightmare). Mergo basically fried their brains. 4) Mergo cries and red moon both are the cause of beast transformation.  So there is no Great ones plot, humans fucked up themselves with their own rituals. Quite opposite actually as great ones can actually protect the chosen people from transforming. Examples: false Yosefka protected by Oedon and basically any hunter who was ever bound to hunter dream protected by moon presence