differing rarities in entity lootpool?

I'm currently working on a datapack that adds a variety of different totems to the game, and currently they are all pooled together in one big pool. This works great, as the player is guaranteed to drop at least one totem, and the totem is selected at random from the pool. However, I was wondering if there is a good way to add different rarities to these drops while still keeping them in the same pool. In the past, I've just added more of the common ones to the loot pool, which technically worked, but I was wondering if there's a more efficient way to do this. I want to still guarantee that the player drops a totem from an evoker, but I want the totems in the pool to have differing rarities. Is there a way to do this? Let me know.