It existed in D2LoD (excluding cure runeword) and still works.
Once the mercenary has the skill prayer, they will boost the healing of mediation and cleansing.
Example : Lets say prayer will heal 20 health per second on your mercenary.
Having cleansing and mediation active on the mercenary would also heal 20 health each, but every 2 seconds instead of one second.
So over 2 seconds, you would be healed a total of 80 health for every 2 seconds in the case the mercenary prayer heals for 20 per second.
It's not exactly the same as doubling the speed since the rate it heals it is not consistent (20 followed with 60 with the previous case), but over the full 2 seconds it is.
tl;dr - yes, very effective.
This post was edited by Djsem on Mar 11 2023 08:34am