Having more than one shield is nearly useless on a defense team anymore.
Having a shield without their defensive skill (AP Down, Impair, Abs Def, Stun) is totally useless on a defense team now.
My general rules of thumb now is to never run more than one shield, as with 6*’s that second slot is more useful as a commander, or to up your damage to deal with said 6*’s.
Also, don’t even bother running a shield without their defensive weapon, as they’ll simply become a punching bag for the enemies AR. This used to be an issue before, but it was small, and you could succeed without it. Now, however, it’s been amplified, they’re either one shot or an AR builder without the right weapon.