I avoid parry where ever possible on DRK. There are a few instances where I could see a potential benefit like large amounts of mobs attacking at once, but these tend to be the exception rather than the rule, and as far as arguing for a dps gain via reprisal/low blow, you aren't going to get more damage than crit respectively while crit is also viable in the OT position where parry would be virtually useless outside of a few specific interaction with adds and such. Crit also has synergy with raid wide dps utility where parry only affects the tank. Considering my personal experiences with hitting enrage at 1% or recovery in regards to a downed dps, the crit increase greatly outweighs the parry. Then there is also phase pushes via increased dps that may negate an entire tank buster or end the fight sooner. If we were talking about a lesser weighted stat vs. parry, like skillspeed, I might be more inclined to agree to a degree.
Also it important to consider that reprisal has a cooldown and any proc within that cooldown is essentially a waste in regards to increased dps further limiting the viability of the dps increase from parry and reprisal. From this stand point if we are to calculate the potential of getting a reprisal proc over the course of 2 minutes of constant attacks that can be parried, there is a max number of reprisals that can be activated during this period and depending on the rate of incoming attacks a few percent difference in parry rate will likely not result in a substantial difference in reprisals available unless parry had some affect on lowering the cool down of reprisal itself.
As far as the mitigation argument via a proc reprisal, parry doesn't really substantiate the cost as I can proc reprisal on demand a very large portion of the time by using Dark dance 3 to 5 hits before reprisal is needed and almost always have it up when I want it. (Try using dark dance during the "jumps" at the beginning of seph ex for instance and you will almost always have reprisal for the tank buster without fail.) With this in mind I get that benefit along with Soul eater crit potential for life regen.
Then there is the healing meta which is precast full damage recovery essentially rendering random parry mitigation a waste of mp on scripted large hits and unreliable in the short term. Even generally speaking, if you increased the parry rate by 6%, it would still be negligible across the course of the fight when compared to the damage increase of other stats and a well thought out cool down rotation.
This is just my opinion however, feel free to load yourself up on parry if that's what floats your boat. I will be sticking to avoiding it for now.