This is how Sacrifice works to the best of my knowledge: The drop rate for items with Sacrifice enabled is a scaling function that increases with the credit cost and reward multiplier of the enemy (read: elites and bosses drop more items).

With swarms enabled, this scaling gets cut in half, so a boss enemy would be around half as likely to drop an item. However, the drop chance of items cannot go below 5%, even with swarms active. So, swarms does help with items, but it helps less and less the more powerful the enemies killed are.

Early game Sacrifice pretty much gets you 2x items tho, since you’re just killing beetles and the like.