Quote Originally Posted by PiedPiper View Post
So, for one, at full i90 your parry stops 24% per parry, not 15%. So, if you had a chance to parry all incoming attacks, it would actually be a little over 6% average mitigation.

Secondly, parry check is preformed AFTER block check, so increasing your block rate lowers the number of attacks you can parry. This means the onion shield actually lowers your total parry mitigation, which is pretty bad since your parry mitigates more than your block does with the onion shield equipped. (Again, 24% vs 20%.)

So, with Zenith/Allagan: You block 24.74%, leaving a little over 75% of attacks you could parry. Multiply by chance to parry, then amount parried, and poof: 4.36% damage parried. + 6.79% from shield, 11.15% total mitigation.

Onion: You block 34.72% of attacks, leaving 65.28% of attacks you could parry, all said: 3.94% damage parried. 10.75% total mitigation.

You lose 0.4% by switching to onion shield.
You lose 0.4% total mitigation but gain about 10% of attacks blocked (at a cost of a proportional amount of those 10% of attacks not being parried), which I'd say is likely more valuable even if those blocks are weaker. The point is to make it more difficult for big spikes to kill you - total mitigation is nice but spike mitigation is nicer, and block/parry rate, not strength, is what helps spike mitigation.

That 0.4% is just going to be covered by what would otherwise be overheal anyway.