This isn't a useless exercise--there are trends in various species. Some species are more prone to docility, and some are more prone to aggressiveness. The exceptions don't make a scale pointless.

I'm curious as to how Irian Jaya carpets score.

I have 40 ball pythons, and not one of them is aggressive. I did have an aggressive female once, but sold her off (with full disclosure).

Hatchling temperament should also be discounted. The baby house snakes I had were the nippiest little things on the face of the earth, but most adult house snakes are docile sweethearts that make great ambassador animals. Many baby balls are nippy, and some are even downright nasty, but most grow out of it.

Pueblan milk snakes are flighty, musking, and occasionally biting nervous little things that barely calm down with age.

Sinaloan milks can usually be tamed and are as calm as corn snakes.

I would put the GTPs and ETBs in the expert category because their environmental quirks are more important than how much help you might need to keep one. They aren't easy to keep, and you do need to know what you're doing.
I understand they can be tamed down if you work with them, just like other species--the problem is a hair trigger response to breath in their face (if you exhale on them, they may bite you in the face), and super long teeth that hurt really bad. Keeping those factors in mind would be important if you were going to handle one--keep the animal away from your face, even if it's tame. ^_^