Rough Example:
Level 1: Sweeper Monk (Xuzhu)
Level 2: Xiao Yao Elders
Level 3: Xiao Feng, Murong Bo
Level 4: Murong Fu, Duan Zhengming
After the 4th level, ranking becomes a bit fuzzy. I don't think we have ever compiled a detailed ranking of people like Murong Fu's servants, Duan Zhengchun's servants, Duan Zhengchun himself, the 3 lower Evils, etc. Perhaps we simply don't have enough information about their abilities, but perhaps we can do better too.
Where does Duan Zhengchun belong? He is often omitted from the ranking system altogether. One part of the novel made him equal to, or below, Murong Fu's servants, and another part of the novel made him stronger than the 3rd Evil. So perhaps:
Duan Zhengchun's servants <= 3 Evils < Duan Zhengchun =< Murong Fu's servants?
Plus there are people like You Tanzhi's father, Zuo Bufan, the old woman servant of Tonglao, and a bunch of previous generation folks involved with the Xiao Yuanshan incident.