is there a point to using Royal authority in your pally rotation?

[Seraphor]

the total combo potency of rage is 640, the total of goring blade is 650 and then another 60 for a total of 710 and royal is 760.
so considering that I value arggo over damage...

Then you don't know how to tank.

Damage = Aggro
You only need an Aggro lead, you don't need to go any further, there is no benefit to having 10x the aggro of the next DPS when you can make do with 2x the aggro.

Your Aggro combo is a tool to give you that Aggro lead or to reclaim it if lost.
Everything after that should go into damage.
Deal enough damage, and you won't lose your aggro.

What you're doing, is no different to a WHM spamming Cure II on you when you're already at full HP.

EDIT: Oh yeah, and a 60 potency DoT over 21s doesn't add 60 potency, it adds 420 potency spread over 21s.