It doesn't matter what the overall proportion of blockable vs. unblockable damage is. It only matters whether a WoG heals for more than a SotR mitigates. I checked WoL, and H-Yor'shaj (25) appears to still swing for ~75k on a paladin - 43k for 10H. SotR would be strictly better while tanking - WoG while just soaking off the DoT, of course.
The critical effect is stochastic - much like the increased block value portion of the buff. What's realistically in comparison in most situations is non-crit WoG vs. one guaranteed block (which, incidentally, also adds DPS). Currently SotR almost always wins.
Part of the problem is that SotR scales with boss damage, and WoG (thus far) does not. If WoG is attractive in 25H, it will almost always be the superior survival choice in 10H and normals. Conversely, if it's made balanced in 10H and normals, it will almost never be useful in 25H.
So, again - likely is a tough sell. WoG is around, but thus far it looks like it's going to be a rare-use tool.
There's nothing wrong with WoG being a situational ability (not that you're saying there is, but there does appear to be a sub-text of disapproval going on here). Everything is situational, really, or will be once the numbers are crunched thoroughly enough to figure out what ability is optimal in which situation. Its pretty much impossible to balance abilities such that you'd literally be indifferent to which one to use in a situation, and even if it were somehow possible, it would be pretty poor game design to create conflicting abilities. So, whether WoG is rarely used will be dependent on how rare are the situations in which its the optimal use of HoPo.
Which ability to use in which situation does indeed seem like it will be pretty clear. If the boss is meleeing you and its melee isn't absolutely trivial, then you use SotR. If there's a break in the incoming melee (boss is out of melee range for some reason, or goes into a cast-only mode, or its a tank swap/BQL thing) then switching over to WoG could be a reasonable choice (to help out with the healing) though if its a burn phase, sticking with SotR would probably be valid, depending on how the mechanics and your raid's capabilities shake out. Of course, if the boss is up flying around and out of melee, you could WoG, but you'd also want to make sure you'll have have enough HoPo to ensure a SotR as soon as it lands.
We don't know any of this stuff yet, so while it seems quite likely SotR will be the "go to" HoPo use, its impossible to say how often we will end up WoGing. In Patch-style fight, sure, pretty close to never. With Yor'sahj, I could see sticking with SotR since you'd probably want to keep doing damage to the boss while he's calling the blobs, and doing damage to the adds/blocking their attacks isn't a bad thing either, but I could also see an argument for using WoG a good bit as well(your damage against the adds is probably pretty trivial, and I doubt they hit hard enough to make the block more valuable than the WoG).
Edit - With regard to stat weights, nice work Theck! An added advantage, of course, with going with the dps gear is that you'd probably do a fair bit more damage with a bunch of hit/haste pieces (even reforged to dodge/parry). Certainly your first priority is staying alive, and it sounds like threat will be trivial to maintain, but tank dps still has value. If you can get 99% of the survivability with dps pieces and up your dps by 20% or whatever, that seems like an attractive choice (assuming the various assumptions we're working with hold). I'll be a little surprised if they let Mastery go live this awful.