Damage will always rule enmity/threat/aggro. It's really just a matter of how to make it play into whatever jobs you choose to assign the tank role to. How to keep that damage in check so that it doesn't lock horns with the DPS and how the tanks should pace themselves in order to be of use to their groups. It's an all encompassing effort, and if you want to get it right chances are everyone will be affected by it in some capacity. So you'd be f*cking with all 20 jobs instead of just 6 or 7.
Or you can just fix the enmity system so it isn't totally ruled by damage dealt instead of f*cking with six or seven different jobs.