Post by PrimeSonic
I don't know where you heard such a thing. Leveling as Discipline is not very different than leveling Holy and the build you would use for leveling is actually not all that different than the old "lolsmite" build.
From my experience: Discipline, as far as leveling is concerned, doesn't shine or feel any different than Holy until maybe level 70 when you can take the following:
Divine Fury For faster casting of majority of leveling spells.
Penance For faster DPS output and considerable healing power
Once you can reach those two talents, you should have the basics for leveling as Discipline. Take any Discipline talents that increase your spell Haste along the way as anything that helps reduce those painfully long cast times is helpful.
As far as a leveling rotation, use of your DOTs is situational. For me, I usually go Holy Fire,(SW:P), Penance, PW:S, Smite, Mind Blast, and then either finish off with wand shooting, another Smite, or maybe Penance if it's not on cooldown anymore.
This was the build I used at level 70. Coming from Shadow, this actually wasn't a bad transition. Sure, I had to relearn a few things, but I was just as effective when soloing as I was before.
BTW: Horde FTW ^_~