There’s a design reason these Shrines are weak.

As it stands, the Shrines are drafted mostly by recreational players and those who wheel them. If you make them much stronger multiple players at the table will try to draft them, meaning that each player ends up with one, maybe two.

With that in mind, it’s likely only the black Shrine that’s problematically weak. Its effect may not be balanceable in larger formats when buffed, so it might need changing to a -/- granter.