The whole thread seems to use the info at start that each point of parry is 0.015% per point, while it actually is about 0.08 %. That's a very significant difference. Every 13 parry give you 1% more chance to parry.

Currently, gearing for parry, a pld can go to about 28% parry rate in ilvl90, while with zero additional parry you would be sitting at 10%. I don't know in what world that seems negligible to me. I personnally which tank i want in my party.

Compare this to the fact that you need about 50 secondary stats (det, crit or ss) to increase your damage output by 1%. It is simple, parry is outstanding. You should definitely look to max out parry on top of having enough acc to never miss a hit. Once you have done that, if you still have a choice, whatever, get some det or crit. Atta boy. In the mean time, focus on what you need to focus: surviving.