Let's step back and look at the reason for this discussion in the first place. The tanks are currently balanced when you look at rDPS. But the underlying claim here is that certain tanks ought to do more rDPS than others to offset the fact that less of their damage contribution occurs under buffs, which then impacts the rDPS of the buff providers. In order to evaluate that claim, you need to be able to quantify exactly what that rDPS offset should be, right? Otherwise this is all just feelycraft.

The exact value of that offset is going to depend on the number of such buff providers in the party. For example, if you're running exclusively with non-buff providers like SAM and BLM, you shouldn't have an offset at all. If you're running exclusively with buff providers like NIN and RPR, then you should have a bigger offset. So you need information on what the 'per buff' offset should be, and then you can try to come up with what the average value should be across all comps. aDPS doesn't tell you this because we have no idea how many buff providers are in the group. That's why you don't see actual dps players quibbling about this, despite the fact that we contribute significantly more damage than you do.

Here's the thing. There are plenty of things that you cannot accurately quantify that may boost dps. SCH's Expedient gives your party a movement speed buff. That may translate into extra uptime in certain conditions. How do you determine the 'equivalent' rDPS offset should be for having access to this action? The answer is that you don't. People only bring these things up because they want to curry an advantage over others. If you balance based off of rDPS, the numbers will be close enough that the better player will come out on top.