You're right, I shouldn't have discussed this topic this way so here is what I believe:
Having enderman farms do not provide shortcuts, but rather another means of leveling combat McMMO skills and gathering resources. A shortcut would be my earlier proposition; if double exp for McMMO skills through donations was a shortcut (this is something I agree with, although I still hold my opinions of that subject aka I want it). Killing enderman, through isolated farms, simply is another means of leveling McMMO or gathering resources. Just like how sugar cane farms are used to level Herbalism efficiently, animal farms for the Taming job and how current mob traps are used to gather resources and fulfill job promotion requirements. Currently, enderman farms are restricted median of use.
In the current state, I do agree that the amount of money earned from enderman can pose as a problem, but I can think of an example that is similar, if not worse, than this. Creating shovels and salvaging them provides a large sum of money with very little effort (the only cost being sticks). This being said, the amount of money provided can be a lot so maybe a decrease in runics earned per kill can be reduced or other methods.
I also want to mention that on my previous post I mentioned the concept of more exp over time. I specifically said over time because hitting enderman compared to other monsters provides a slight variance of experience gain. The only difference is that enderman have much more health than normal mobs and this is important in terms of spawning. If a chunk is filled with a certain number of monsters, new monster will not spawn until they are a chunk away (which I believe is 16 blocks in all directions. Keeping efficiency in mind, spawners are placed, in general, 20ish blocks away to maximize spawns and to kill with ease. Because enderman have more health, you can keep them at an optimal distance from their spawning platform while having plenty of health. Since McMMO combat skills give experience based on damage (multiplied by the monster type), enderman gives the most potential exp per kill.
For these reasons I think enderman farms should be allowed. I dont't believe including them will cause shortcuts, but rather another mean of getting McMMO exp and resources.
I also want to thank you for considering the subject. It is a subject that you could have easily dismissed, but you're willing to take the time to discuss. Appreciate it.