He's saying Defense sucks because, no matter how high your defense gets, NMs of any worth are still going to be capping or near capping cRatio on you. And, once cRatio is capped, no additional damage is taken by having lower defense.

Nutshell: It doesn't matter if your Defense is 700 or 7, if the monster is capping cRatio then you'll take the exact same amount of damage. QED: Defense is utterly worthless unless you're actually making a significant dent in cRatio, which is quite literally impossible on the vast majority of harder NMs and not worth doing on weaker NMs that would die in a minute or two in DD gear.

Edit: Oh yeah. Counterstance reduces more damage than any non-Ochain shield ever will. Shield is an absolutely horrible method of mitigating damage and requires an Ochain to be at all useful.