Holy site holding slots

I'd like to suggest that every holy site should have at least three holding slots. If it doesn't there's the risk that the AI, or player by mistake, builds something else there and thus blocks the religion from getting a full holy site bonus. An example would be Lonely Light. It has only two holding slots and starts with one castle and one empty slot. If someone builds a city in the second slot the Drowned God faith is handicapped for the rest of the game (except on the odd chance that a looter levels a holding to the ground, an unlikely proposition at best).