Where did you get the idea that you get to carry the unactivated overshield around with you? I've not seen a single instance of gameplay where the powerups work like you're describing. It's just you have to press a button while on the powerup instead of walking over it to automatically activate.

Also, where did you see Promethean Vision? Did you watch without listening to a thing the announcers were saying? That was a new spectator feature. It would not make any sense to have all enemies visible through walls 100% of the time.