In response to the OP.
The bottom line is that you are choosing between a minor boost to threat over something that is a very real survivability boost. I know your tracker is not showing that atm, but give it time.
There are at least four wipes I can think of off the top of my head that AD has prevented recently for me. The first two were against magtheridon oddly enough. One time I went down to 487 health after taking an AD reduced hit, and another time I went down to just over 1000 after taking an AD reduced hit. I had close to 22.5k raid buffed and had ironshield potions/shammy crit heal buff so his hits were weak enough and my health high enough to make the talent useful on that fight.
The difference AD made was between yet another wipe with our avoidance loving, low stam bear tank and my guild at the time's first kill. Same situation with that guild's second kill.
The other two I can think of have been in the last two weeks. The first was when we unexpectedly pulled a murloc pack on the way to tidewalker and I was hovering at 3k-1k health for a good 15 seconds as healers were spamming on me while I tanked the whole pack in my non block value set.
The second was tanking the shaman add on the fathom lord fight and there are numerous times when AD has saved me against that monster of a shammy. Seeing my health at 400ish.. or 700ish after taking one of the cataclysm bolts + windury is always fun indeed.
Each one of these situations my healers were stressed. These were progression or "oh %$^&" moments where things weren't going smoothly. If I didn't find myself pushing things to the limit in heroics, raids, etc I probably wouldn't value this talent as much. Seeing as I tend end up pushing the envelope rather often, I can't recommend tanking without it

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Zeal without wisdom is folly