Mastery, i can't see difference

Okay i'll start with linking my armory
http://eu.battle.net/wow/en/character/R ... tis/simple .
I'm focusing on mastery since everyone says its the best stat, however i've been watching damage taken (from recount) and noticed that the 2nd tank takes less dmg (I took 27mln and he 21mln damage for overall data, ofc i was also tracking every single try, and on most of them he took less)
His armory : http://eu.battle.net/wow/en/character/r ... ela/simple
I'm at 10% block chance higher and about the same for summary dodge+ parry. So... what's the deal, is mastery overrated or maybe recount is failing at calculating damage taken?. On the side note i was starting encounters and some wipes were quick so he didnt took any damage at all (well very minor from lava spit) on magmaw, but still the difference is too big (and as I said I also checked "current fight" on most tries).
It's really bugging me, I'm trying to min/max my character and bah
And one more question, which trinket combo is the best right now, I just won Symbiotic Worm, and I'm farming Baradin reputation for pure mastery one dunno which one of them will be better (yeah I know that differs from fight to fight).

Well, start with comparing number of hits taken. Did you take more? If so, then your damage taken will probably be higher.

Then there's RNG. If your sample size is relatively small, it's easy for numbers to be skewed. You may have been particularly unlucky.

What about special abilities? Did you take more special, stronger, unavoidable hits?

If you take out the special attacks and dots and such and just look at the regular swings, you should be able to see if you take more, or less, damage per normal swing.

There are a lot of factors to consider, such as holy shield uptime, mitigation from armour, and random chance. Those factors can colour the results, sometimes quite dramatically.

Watch Omen, see who has the most threat on the most mobs.

If you are working harder than him on trash pulls it's easy to take a lot more damage on the over all.