As a WHM that used Regen II/III extensively during the 75 cap years, it saddens me to see that there's really no reason for WHM to cast any of the Regen effects, period, because SCH can simply do it better.
If that is the case, let's get rid of the Cat 1 Regen Merit Point choice or replace it with something that would be worthwhile for WHM to even choose that.
SCH easily gets 58HP/tick Regen IV that lasts 1 min 48 sec (at Level 99, Light Arts, and Savant's Cap +2) while WHM can only get up to 44HP/tick that lasts at most 1 min 18 sec (and requires Marduk's Tiara +1, Cleric's Briault +2, Orison's Mitts +2, and 15 merit points). And that's not counting the fact that, if SCH uses Tabula Rasa, they get 70HP/tick for 2 min 21 sec.
I'm not asking for a lot, but simply make it so the difference between SCH and WHM's casting of this is not as big.