Also, an elite/champ (or two) will typically get CCed so using AoE for threat generation is limited at times. If I'm not judicious, the healer will get overwhelmed.
There are also times, like in Aurora Cannon, when we need to kill the NPC healers first. I'll bet this is an example of allowing the DPSers to do their thing, while I hold aggro on the main pull target.
I've noticed that a fair amount of AoE seems to avoid CC'd mobs (at least on the tooltips).
Also, coming from almost exclusively a tank for the past 6 years, the fact that you want to be better means you're going in the right direction. Keep doing what you're doing and look for ways to improve your game in your playstyle. Thank you for taking the time to better yourself for the benefit of others.