First off, just to make sure we're all on the same page, when folks are advocating mass pulls, they're NOT talking about leveling dungeons. They're talking about level 50 dungeons and higher. With that out of the way:
This is flat-out, mathematically incorrect. Aoe DPS abilities are designed from the ground up to deal more damage the more targets are hit. It's a simple fact. No matter how terrible your DPS are, they will deal more damage to a big group with their aoe skills than they would large or small groups with single-target abilities. As for mob packs being far apart, it makes little or no difference. The healer can keep you alive during even the longest of gaps, so long as you establish hate on every mob along the way (Flash, Unleash, Overpower work fine, or even single-targeting each one with a thrown attack - either will give you enough hate to hold all the mobs even with the healer curing you).
As long as you're the one doing the dancing and not your DPS, it still works out for the best. The only time this should be considered a factor is if you have melee DPS with you, and even then most aoes are frontal, leaving your DPS free to attack while you do all the dancing. Additionally, even if you accept this as an excuse, most dungeon mobs do not have aoes you need spend a lot of time dancing around. Sastasha (Hard) is probably the worst case of this, but it is the exception, not the rule. As for your example, Stone Vigil - there's hardly any dancing at all to do in Stone Vigil (Hard), and if you're talking normal mode, again, it doesn't apply to this discussion.• Too much AoE. Stone Vigil comes to mind, but there's others out there as well. If I'm spending more time dancing around AoEs than actual tanking then that just makes it harder on everybody. Too risky.
I find your lack of faith disturbing... Seriously, though, don't underestimate sprouts. Many of them are folks working on an alt, and even genuine sprouts, more are decent healers than are bad. While it's advisable to do a few test pulls if you're uncertain of your healer, don't be afraid to ramp things up if they measure up. You're only doing your healer a favor by making them push their limits; they will be a better healer as a result.• Lack of faith in the healer. If the healer is a sprout, no way in hell I'm doing it. If I inspect the healer and he's not overgearing the dungeon we're in it's a no-go for that as well. As one who has been on the receiving end of this, if my gear wasn't in tip-top shape and I wasn't very good me and the tank would never been able to pull this off, not something I could say about a lot of other healers out there.
The majority of healers or DPS are smart enough to bring strays back to the pack, but even for the ones that aren't, Provoke followed by Weapon Throw / Shield Lob / Unmend will usually bring it back to the fold - or at least distract it long enough for the DPS to finish killing it. If you've been rotating enmity correctly, it's rare that a DPS will manage to pull away a mob that isn't already on the verge of death - and if it's going to die in another second or two anyway, just let them tank it until it does.• Lack of discipline. If at any point during the pulling someone else catches aggro - including healer aggro - for whatever reason it brings everything to a screeching halt, since I have to now go back and pick them up again, slowing things down and me taking unneeded damage before speeding back up again. Again, not worth the effort.
Wipes are very, very rare. So rare, that the risks versus the returns pay off in the long run. A wipe is no big deal - even if it makes the run you're on take longer, getting into the habit of big pulls will save you MUCH more time in the long run.• A lack of dungeon checkpoints. If we wipe, it's going to be a long run back, even with checkpoints. Basically one step forward means two steps back if we wipe.
Nope. The reward is faster completion of dungeons. I don't think there are many tanks that brag about faster runs. Fast runs are normal and expected. It'd be like bragging about eating breakfast, or about driving your car to work. This game has aoe DPS abilities for a reason; against two- or three-mob groups, those aoe abilities usually provide little or no improvement in damage. They were designed with the expectation that a group will be fighting six or more mobs at once. How many mobs you choose to fight at once is up to the tank to decide, based on confidence in her own abilities and her confidence in the abilities of the group that she's with - but a tank should ALWAYS strive to pull as many as she feels able to handle.Basically, the only reward for doing that is bragging rights, not worth it in my opinion.