There's no real reason tanks shouldn't have a higher reward for better performance. We've already seen that tanks are not having an effortless time maximizing damage. If that were the case we'd be seeing tanks reach their maximum dps with greater ease than dps jobs, but the percentiles show that tanks are very on par with dps jobs in terms of skill to damage gain. The only difference is that the tank role receives proportionately less damage gain for the effort.

So give tanks more to do besides dealing damage, some say. Kind of like healers have to heal? Okay, sure, but let's take a look at healers. Going by current numbers Astrologian sees a damage increase from 3.7k to 8.8k from 10th to 99th percentile. So not only do healers heal, but they also receive the same damage-for-effort reward that dps jobs have. Moreso, in the case of AST, because I'm not seeing a single dps job with a damage increase of 5k from lowest to highest performance.

Just to oblige I did check E2s specifically, and Gunbreaker's numbers barely change. Damage gain from 75th to 99th is 6.6%. 50th to 99th is 12% and 10th to 99th is 31%. Samurai sees damage gains of 6.8%, 12.6% and 34% respectively.

Paladin, the "easy" tank, sees a damage increase of 35% from 10th to 99th in E2s.

Dps and healer jobs both see much greater damage rewards. Tank is the odd one out here.