That's a bit excessive not your avoidance, but your lack of health. For instance if Magtheridon were to ever hit you with an Autoattack and a Cleave, you'd almost certainly be dead. This is why I'm not a big fan of stacking avoidance or effective health for that matter. Often we hear folks talk about avoidance is better than effective health or vise versa. The problem is there needs to be a context when people say that. There are thresholds to consider, especially on the effective health side. For instance, when you are at a point where 2 successive hits will kill you from max health, you are taking a tremendous gamble, because you are going to get hit twice in a row at some point no matter what your avoidance is.
At the same time, if you let your avoidance get too low, the rate of incoming damage can be quite high and difficult to heal through, and if your healers can't keep you topped up the inevitible spikes can be a problem.
The prince really favors avoidance because his ability to burst comes via multiple attacks, and crushing blows aside, you can pretty consistently minimize those with lots of avoidance. I mean he really needs to land quite a few hits in a short amount of time, since his individual hits aren't that hard. 16K health is plenty to tank him, hell the first time I tanked him back in mostly blues and when the Karazhan epics kind of sucked I didn't have quite that much health and way less armor than you have. So he becomes trivial because your health is above a reasonable threshold for the type of damage he can do, and you are avoiding tons of his hits which reduces spike frequency.
That changes though when you go to the 25mans or even some of the ZA bosses, where they can hit very hard and with specials can do so right on top of an autoattack. Once your health is to a threshold where you can survive a reasonable amount of time (relative to the boss' attack speed and power, often 3 hits is the rule of thumb applied here) without being healed, then looking to favor some avoidance can help, but even then there's no reason to just blindly put dodge gems on everything.
Anyhow, if tanking some of the big hitters is in your future, I'd really recommend looking at a more balanced gearing strategy.
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