Agreed. Once you've cleared something, and are able to consistently tank something without having to worry about being killed, more mitigation does nothing aside from allowing you to flex ePeen. Granted, I honestly don't do anything but kara and the early 25s anymore, but take kara for example. It's an easy zone. Myself and the people I've ran with have been through it a thousand times. I can push my effective health set and have 20k HP, I can use my avoidance set and sacrifice about 4k hp but gain about 20% avoidance and avoid 60% of attacks, or I can put on a threat set that will put me at that same level of HP as the avoidance set, but instead I can have a large amount of block value and other threat stats. The difference is that, in terms of the pace of the run, the first two sets do absolutely nothing. I'm not going to die in Kara from damage intake. Honestly. I can't remember the last time I got gibbed in Kara. All those two sets will do is let me flex ePeen and feel cool.
On the other hand, if I throw that threat set on, I'm still not going to die...the difference is that I'll be able to push in the low 1ks easily on average, and spike higher than that. It's amazing how much more quickly it makes runs go when the DPS can push their damage more, and make mobs die sooner. I normally run things with people that are old friends from raiding, and thus geared far beyond what I am now, so I honestly have to take this tactic anyways, to be able to keep up. It's definitely nice to be able to hear 'Mike puts out some monster threat,' from people that are sitting in T5+ gear, as well. Using DPS pots/consumables to push threat on farmed content is hardly a waste, and it has nothing to do with having agro issues. If the fight isn't designed for a tank having a huge threat lead over DPS, good DPS classes will ALWAYS be able to blow you out of the water on threat if they choose to. It's just the way things work, and it's the reason why we use threat meters. If someone thinks otherwise they're either jaded by how good they think they are, or aren't communicating with their DPS the way they need to be.