The reason I think the order of effectiveness of these from the previous post besides being pointed out in effectiveness by staff is because that is the order of highest % chance to happen. So if you increase the skill level of those skills thus increasing the effectiveness of that skill. Here is an example of how I THINK it works.
Assume block/dodge skill is 10% of all incoming attacks and +20 skill mods gives a 10% increase in the skill. This would then give you a 11% chance to block/dodge thus an overall gain of 1% avoidance.
Assume Parry skill is 5% of all incoming attacks and +20 skill mods gives a 10% increase to the skill. This would then give you an a 5.5% chance to parry, thus an overall gain of 0.5% avoidance.
From my extensive parsing when I was tanking lots of different things I somewhat remember misses being around 35% of avoidance block/dodge avoidance being around 30% of all avoidance, parry around 20% and riposte less than 10%.