Your argument is misleading. A warrior going from 25% parry to 26% is now mitigating damage from an extra one hit per 100 swings; a paladin with 25% block and 25% parry going to 26% parry is now mitigating damage from an extra .7 swings per 100 (assuming your numbers are right; I didn't double check them). It's an equal increase in the relative number of mitigated attacks, true, but if both tanks have the same parry percentage and parry strength, the warrior will gain more absolute damage reduction. Parry is better for warriors, assuming both classes have same formula for how it works.