nykken what class do you play? block is a massive amount of damage mitigation, right now warriors can block over 5k with the right procs and a at least 1k when geared in epics. if you don't think thats a large contribution then theres no way any one could trust the rest of your math.
I play a warrior, the class who's chance to block doesn't matter 10 seconds out of every 40, these specific 10 seconds are probably the 10 seconds where those 5k blocks are possible. We are also the class with probably the most block value who still tend to only block about 1/5th the damage on an incoming attack from a boss. I understand chance to block is fairly nice, definitely much nicer than the worthless stat it was in BC, but it still is fairly meh on a hard hitting boss.
More situational for armour than stam because not every boss I tank or trash I tank only does melee damage?
Having more HP works for melee and spell damage, thus less situational than armour only trinket. The same goes for Charge, more % chance for enemy to miss you, more dodge, more parry.
I'm not saying armour is useless, but most of the time I'd either a) have charge+essence on b) have charge+talisman on or c) forget to swap to the armour trinket.
paladins typically have more block, and a much higher block chance than warriors..
and if you think block doesn't help you need to look at some math. its an amazing stat for everything short of the drakes and patchwork.
fine, here's some math.
Assuming there are no diminishing returns, repelling charge provides .68% chance to miss, dodge, parry, and block. Miss, dodge, and parry add up to 2.04% in total. For it to provide double the damage reduction of defender's code, which i think is more than a fair request since the code seems to provide more than half the eh of a trinket out of a heroic, then the .68% block needs to block at least an average of 58% of the incoming damage. Assuming you block an average of 1500 damage including chances to proc critical block and glyph of shield slam is up, then the average hit from a mob would have to be at or below about 2600. Outside of trash, this is a ridiculous number to hope for.
And this is before mathing out the diminishing returns on parry and dodge, which i suspect would reduce those chances by about 1/5th, or the fact that using shield block diminishes the effect of chance to block by up to 1/4th with perfect usage.
The way I would look at it is this. If no other tanks want it, take it, use the dkp, pick it up. You do not know when something like that could come in handy. Besides, our job as tanks is to have the diffrent sets of gear to to take on all types of content. So to disregard an item that could in fact serve a purpose in a fight in the future imho is not the brightest idea.