Averages reflect the vast bulk of game content. Boss fights are a comparable minority, **and a smaller minority yet are ones that severely stress a tank's survival and healer resources. ** They're out there, but from a time perspective, something like 95%+ of one's interaction with the game falls into encounters where the statistical average is applicable and useful.

And

**those** are the ones you need to optimize for. If they're not really a stress anyway, you'll be perfectly fine in under-optimized gear.

And really, this entire discussion boils down to relics, because there is precious reason otherwise not to have a single tanking gearset optimized for one's particular class (there's an easy-to-calculate mathematical "best", from which any deviation statistically means more damage taken). ** One is never better served by having more Defense for one particular fight, and more Shield for another.** Other than ensuring sufficient HP (trivial at present), the math doesn't support a lot of customization.

False, it depends on the attacks used by the boss. If it's using M/R E/K attacks defense will have less value since an attack that gets trough the defense will be mitigated more by armor and shield, but if it's using M/R I/E attacks each defended attack will provide more damage reduction.

That's what's messing my calculations up at the moment - I want to optimize for Kephess, but I'm not sure what his balance of attack types are, so I'm going with the optimal values assuming only M/R E/K and then arbitrarily raising defense a bit when I mod my gear.