The shrines for other gods only require a single NPC kills for every manifestation of zeal. All except Ymir.
For example with Mitra, one NPC kill gets you 1 living essence which can be used to make 1 ambrosia and 1 manifestation of zeal.
The exception is Ymir. It requires 5 NPC kills to get 5 ice shards to change in to 1 Ice and 1 manifestation of Zeal. So it takes 5 times the effort to get a bubble if you are using Ymir which is just insane.
My guess is that when the game was changed where the Ymir hoar frost hatchet no longer could get ice shards from trees, the ratio for ice shards was overlooked.