What you also have to take into account is the fact it always felt awful to use your enmity combo, and not just because that combo had lower potency, it also had an impact on the rest of the rotation for the rest of the fight. Paladin lost MP gain which delayed Requiescat/Holy Spirit, which could also cause delays to Fight and Flight, Warrior lost beast gauge gain and depending on timing, could drop maim and/or the slashing debuff, Dark Knight lost Blood and MP gain. I suspect this also played a role in wanting the DPS to use their enmity reduction tools.
In theory, you could solve that by having the enmity combo also generate the resources for each job, they would just have weaker potency. At this point, I would start to question why have the 2 different combos in the first place, but others might have a differing opinion.
This is the issue with this system. Only one tank. This means, you have to design content that only allows for one tank. If a boss has adds? the DPS has to be able to survive them, so they will be weak. Make them strong enough that a tank has to pick them up, then you run into other restrictions, being damage taken, boss positioning being messed up because of picking up this add etc. It sound like a limiting system, but others might disagree.