Ah hah! I guess I misunderstood the Wiki, that makes much more sense. For some reason I thought the fireballs could still AoE me even when my grounding totems were there, so I was trying to frantically run towards the dragon (and running out of range of my grounding totems) while he was shooting me from the air. This will help immensely.

So I will try again tonight, and this time I will do the same thing I did before, but I will only run down the ramp after the dragon finishes throwing fireballs and starts to fly around, the i'll run halfway, drop another set of grounding totems, wait for him to stop again, then run the rest of the way, then drop more grounding totems and start nuking him in the air.

I'm guessing when he lands at 20% or whatever, ele mastery + vengeance trinket (+120 spell damage?) + bloodfury (now up to +135 spell damage or something) + 5x LB/CL/whatever should be more than enough to take him down before he can significantly damage me, and then if I understand it correctly I can rest to full before nuking the rider down also?

That sounds like it will be even easier than the first boss if I do it that way. I will try tonight and report back! Thanks everyone!