The only area I can recall discipline being a "bastard" or "red headed step chield" would be on the actual healing area. You can say what you want about having a powerfull shield, but pw:s still got a 15 sec stopping mechanism for each target and even being able to shield more than one obviously your heals on their own will be relatively weak.
Just to put it in - this is mainly ranting atm
Now adding that its not meant to heal more than "one" target at a time the heals themself ought to have more punch - its not even needed to place talents in the holy tree further down to "balance" out since disc will have to take a load of talents just to get whats needed in discipline allready. Now I may be underestimating the 10k aegis - when stacked (which means the actual heals need to be powerfull enough to not get absorbed by blows and so on to stack enough), so maybe its not so bad there. But all in all a disc priest should be able to single target as well as a paladin - afterall as they said with dps "hybrids shouldn't do as much damage". Disc priests will allready see a decline in mana regen after all - where I doubt paladins in most cases will care much that they loose spiritual attunement since most of the regen there is from crits anyway.
could come up with plenty examples how paladins can just spam their heals, but really we all know them too well.
So in short - more healing power to disc