Okay.

DEX = Block Rate\Parry Rate

STR = Block Potency\Parry Potency\DPS\Enmity

If you're blocking all the time for very little that's great for auto-attacks. Those attacks however are very /easily/ managed by healers at high level with Regen and Medica paired with your abilities.

If you're about to eat a high damage attack - you /might/ block that single high damage attack and yes you'll certainly have a better chance of blocking it by raising your rate, but your block potency is low.
Block potency is going to scale with damage - I /know/ that I can boost my block rate by 60% in a pinch, and if I do block I will block /much/ more of that single high damage attack.

You have CDs that also further reduce this damage - and a static reduction to damage by using Shield Oath. By focusing on STR you're raising your DPS and reducing enmity strain which allows healers more freedom to use their high enmity generating cures when they /need/ to use them.