I remember that thread now, at least, I remember reading Nightfish's breakdown before. He may have reposted what he had written before. There's a couple of problems with it.
I'm going to use level 92 as a level that a typical guardian plateaus at because I believe it can pretty easily be reached just by doing Pindleskin runs.
The amount of dexterity needed to maintain 75% blocking increases by 2 dex per level, so maybe he was using a lower level as a benchmark. Realistically anyway, a non-Stormshield sorc will have a 60% shield (Rhyme/Lidless) and require a total of 245 total dexterity at level 92, or 220 dexterity added from points or items. A sorc using Stormshield will lose more points into strength than save from the higher blocking.
A second problem is that with 50% physical damage reduction, health is twice as effective against physical attacks. A 400 increase in life will be worth 800 hit points against physical attacks, because the attacks are only half as effective.
A third problem, like I said, is that the value of vitality points can be multiplied not only by %DR but also by Oak Sage charges and Call to Arms on switch (although these runewords are difficult to acquire, they are by no means impossible especially Heart of the Oak).
Lastly, there are some sources of damage in the game that are so high, blocking is useless. Pindleskin's charge. I have no idea how much damage it does, but it one-shotted a 707 hit point sorceress that had no %DR and 75% blocking. Sure, 3 out of 4 times I would have blocked that, but it only takes that 1 out of 4 times. Vitality needs to be high enough to survive at least one of those attacks otherwise blocking is useless. It would be ideal to be able to survive a couple of them.
Being able to survive 40 arrows instead of 10 is nice, but that's misleading. I often do the happy feet thing where I run back in forth to avoid the incoming arrows from hitting me while I wait for my casting timer. Since blocking is reduced to 33% (I think), so it's more like 15 arrows not 40.
Plus there's always gloams...