I don't know why, but some posts suggest hope is easy to counter with creature control...
Upgraded it gives 2 protection even without any light emitting creatures! An indestructible shield with 2 protection is very good in itself, greatly reducing damage from Fire Queen, Incarnate, Ferox, Morte, burrowed shriekers, puffer fishes etc. making it great for early game, before you can play those light emitting creatures (of course if you have an early source of light, so better for rainbows than FFQ for example). Add some SoG's and sundials, and it greatly helps to survive until you can play some quinted source of light, luciferined drags, light nymph+skeletons, whatever... it seems to be equally powerful as a bone wall in late game, but better in early game.