One big problem with tanks in OC specifically is tank mastery which bundles in a hidden potency nerf to tank damage calculations but specifically doesn’t apply to phantom actions, and then phantom actions have such deceptively high potency that it ends up basically removing tanks only real downside which is their damage (for example I have all +1 gear on PLD, blade of valour is listed as 1000 potency. A critical direct hit with it does 95k damage give or take. A 1000 potency hit on a DPS critical direct hit would do about 130-140k. Then comet, a skill listed as having 500 potency with my +1 gear does about 240k damage)
Then there is the fact that that there isn’t a single phantom job that provides both sustain and damage to yourself. Chemist and freelancer provide sustain but no damage options and geo provides damage and sustain but it’s basically impossible to get meaningful damage out of bell yourself as a non tank because the raidwide damage has to be scaled specifically to DPS not playing GEO.
So the tanks only downside is removed. The other jobs have to trade any damage increases to get sustain and the downsides of strong jobs like oracle and beserker feel like they were balanced around tank sustain