I'll put it this way: all tanks and healers are going to treat every fight as if you will never Parry anything.

If you happen to Parry, great. Won't actually change how people react. Healer will still throw the same Cure at you that they would've anyway.

All raids, bosses, etc are scripted fights. There is a set rotation. The majority of cooldowns and heals are used proactively, not reactively. Because of this structure, it's pointless.

Also parry rate is not 25%. You can't possibly reach 25% with current numbers (aside from cooldowns). It's like 8%.

And your Crit/Parry comparison pales because Crit scales much better, AND affects the potency of Crits (parry is constant 20%)