@Meddler, Ardent Сenser?

Personally I like it the way it is. It's not going to be useful for every support but there are a few supports in which it's very strong on. Karma can get a teamwide shield every 30 seconds (less than that with her passive in a teamfight) which makes taking towers for her team incredibly easy. Soraka's heal is on such a short CD that if she has an AA based team she can make good use of it too and Sona has a shielding aura to her heal making it possible to hit everyone with the AS buff as well but on a much shorter CD than Karma. For these supports the passive can make a big difference in a teamfight. For other supports like Lulu or Nami it's not going to make as big of a difference.

Really it's one of those situational items. I don't think it needs to be changed I just think you need to be aware it's not meant to be built on every support or in every game. Don't build them if you're not on par with the other team, or if by behind you mean you have a lot of ADCarries (someone like an AA based jungler) who have AD and not AS.