You can't stack block, so using cover then Sheltron, like you could in SB (o12s anyone?) to mitigate a crap ton through the innate 20 percent mitigation it had plus a block of about 30 percent at end expansion levels was really good when used well.

Cover needs the damage reduction, or rather, we need more instances to use cover on a non tank teammate like Guardian's missiles. The damage would be tuned for a DPS or healer to eat it, meaning it'd tickle a tank, and cover would be valuable to use. Or have busters act like in o12s where they apply a vuln to the first person hit, then you could cover, reroute the damage to yourself and receive only the base damage as you would have no vuln like you could with Target Analysis in Final Omega.

It'd be something that you COULD bring PLD to for even more optimization, but didn't HAVE to, making cover valuable, but not necessary.