I can’t tell you how other sources came to their conclusions.
I can tell you that we run thousands and thousands of simulations to get data across all possible builds, then we create a mathematical model based on that data. The model smooths out the noise and predicts how well any set of gear will be.
So, in our simulator and model, shambler sims higher and scores higher. I tested that item a lot on beta because it seemed ridiculously good for unholy due to it getting multiplied by mastery. The low proc rate can be annoying, but it sure does hit like a truck.