Why Avoid Parry?

[Ralvenom]

but won't it help to smooth out incoming damage when there are a lot of hits coming in? And to that end, isn't Parry then the best stat a tank can get?

There are no boss fights where there are a lot of hits coming in, so why bother. On large dungeon pulls (literally the only time you get hit a lot), you should be using several CDs anyway, which means you don't need a lot of parry to deal with that (common) situation. Hell, if you really do need mitigation for physical attacks, WARs just pop Raw Intuition, PLD pop Hallowed Ground, & DRK can pop (although they rarely would) a Dark Arts enhanced Dark Dance. My point is, if you actually NEED lots of mitigation, then you basically have it via defCDs.

The current boss design is such that parry doesn't help, because the damage is predictable (and therefore easy to deal with, if you just pop the correct CDs). As such, it is more beneficial to have the minimum HP required & then just stack crit, which allows you to add damage to the group.