Nice analysis but I got a different opinion on this. Im talking about CONSISTENCY. If you got 52 dmg reduction like me on my tank and u get a 20K hit, you will only receive roughly 10K damage, EVERYTIME. Shield is only a chance. Even if you got 50 percent shields, you might as well get the whole 20K if RNG hates you. Furthermore you dont have 100 absorb, so even if youre lucky only half the dmg is absorbed. But high HP also increases survivability, so the healers can leave you longer unattended without you going down. Also depends a lot on class I think. Im jugg tank, so I dont get shield bonus or anything, can never reach those insane shield stats of assassins or PTs, so I basically rely on my high dmg reduction, HP and my defensive CDs.
Mitigation up to a certain threshold is necessary for many top end operations to make healer job easier, especially on hard hitting encounters like Dread Guard - HM EC Kephess. Endurance too of course is important but if you see past the RNG factor ( Nobody is really so unlucky as to prefer endurance over 50% shield because their shield never mitigates) But of course after a certain threshold, which is nicely presented in noxxic.com, it doesn't reward as much as it used to therefore at that point it becomes more and more prudent to stack Endurance instead. a jugg/guard tank can easily reach 27-28k hp even if he invests on these mitigation stats.