Logic behind Guardian Rune Passive

Trying to understand why it exists.

I happen to walk within 175 units of an allied champion, some random enemy ability or auto attack happens to strike that allied champion, Guardian's shield and move speed buff go largely wasted and the ability goes on cooldown for nearly forever.

I suppose you could use this rune on a champion that has no shield, and it might count as a shield to trigger Ardent Censor, but if that was the intention behind this passive, there should be a way to disable the passive completely if your champion has an ally-targeting ability.

The rune is a great idea, but the conflict between the passive and triggered effects of this rune are just so bizarre and significant, I'm surprised it released like this at all.