I've only had crap shields, but does block ever show up on shields in this game? Since it's an equipment slot that could be taken up with a weapon for dual wielding or switched to a 2 handed weapon, it having only additional physical armour makes it so it's wasted after that bar is depleted, and less useful the longer the fight goes. So do any good shields eventually give block?
I mean.. it's about whether you want to be tankier or spikier. Shields provide more defense. Yes, that defense can get used up, just like your hp, but it is refreshed each time you enter a new battle. Also, shields can have other stat's on them, like bonuses to skills, or attributes, so even once the armor on them gets consumed by blocking damage, they're not completely useless.
