Was there ever any attempt to reach some sort of agreement on what appropriate usage would be?

I imagine if this was the real issue, then WPEngine could probably sort out some fair solution to not use more than their fair share. I dont know much about this ecosystem but surely a caching proxy is not hard to setup.

However reading between the lines, it sounds like the real issue is that WPEngine is more succesful which is making other players jealous, who are using their control over other parts of the ecosystem to give WPEngine the middle finger. In such a case its not really about resourse usage.