The more complex a monster is, and, likely, the higher its CR, the more of these judgment calls come into play. Which is to say that it is more than just a math equation and there are numerous judgment calls that are made. First, I’m not sure that Wizards would show us all the secrets of “how the sausage is made”, and second, I think there is a good deal of “art” in the determination of a monster’s CR. One of the assumptions many/most people who level these complaints seem to make is that the guidelines for determining a monster’s CR given in the Dungeon Master’s Guide represent the entirety of the parameters considered by Wizards of the Coast when determining the CR of a monster.
Some of this criticism may be valid, however oftentimes these complaints reveal more ignorance on the part of the person complaining than faults of the system. Quite a bit of criticism has been leveled at 5th edition’s CR system.
