Point blank, if you're wearing an offhand with 10 AC and 175 hp/mana and 35 sv vs all, you had better be somebody who isn't worried about being hit in the first place. When I look at Reflective Shield, it pantomimes at me like it's drawing a bow and shooting arrows, and its glassy surface shows phantom images of throwing and joust back-stabbing on a fight where something both WWs and requires massive resists and stun resist. Which at this point is like, what, one fight in the game about two tiers previous, lol? If you're a tank who isn't going to need to be wearing a shield for a fight, you whip out that 2her and git to work.
tl;dr: It's not for tanks. It's for the other people on it.