There has to be a line somewhere. They had chosen to go with "Wishes don't work". Companions get a pass because they aren't actually getting anything else from outside the game; just themselves. That is the line they have drawn. I personally would have preferred even Companions not working but such is life.
The efficacy and/or power level of this card shouldn't really be a determining factor. The nature of the effect is. And this effect offers no built in restriction to deck size. Companions do as they add 1 no matter what. You blinking this a bunch of times and getting 100 new Angels in hand isn't exactly bound to happen but the possibility exists and someone will do it (it is EDH after all).
The efficacy and/or power level of this card shouldn't really be a determining factor. The nature of the effect is. And this effect offers no built in restriction to deck size. Companions do as they add 1 no matter what. You blinking this a bunch of times and getting 100 new Angels in hand isn't exactly bound to happen but the possibility exists and someone will do it (it is EDH after all).