:: Warning :: This post contains mathematics; TL;DR section at the end

Hrmm... there was me hoping to crush that argument... but alas~

As far as efficiency numbers go...

Regen 3, 20/tick, 64 MP, 5s casting time
Regen 3 (no gear, no merits - 400hp) 6.25 HP/MP
Regen 3 (no gear, merits - 500hp) 7.81 HP/MP
Regen 3 (gear, no merits - 575hp) 8.98 HP/MP
Regen 3 (gear, merits - 700hp) 10.93 HP/MP

Regen 4, 30/tick, 82 MP, 5s casting time
Regen 4 (no gear, no merits - 600hp) 7.31 HP/MP
Regen 4 (no gear, merits - 700hp) 8.53 HP/MP
Regen 4 (gear, no merits - 825hp) 10.06 HP/MP
Regen 4 (gear, merits - 975hp) 11.98 HP/MP

Low Quality WHM Cures
(601 power)

Cure 3, 252HP (88SS), 46 MP, 2.5s casting time
Full cure and no stoneskin, 5.47 HP/MP
Full cure and stoneskin, 7.39 HP/MP

Cure 4, 508HP (177SS), 88 MP, 2.5s casting time
Full cure and no stoneskin, 5.77 HP/MP
Full cure and stoneskin, 7.78 HP/MP

Cure 5, 885HP(221SS), 135 MP, 2.5s casting time
Full cure and no stoneskin, 6.55 HP/MP
Full cure and stoneskin, 8.19 HP/MP

Cure 6, 1096HP(274SS), 227 MP, 2.5s casting time
Full cure and no stoneskin, 4.83 HP/MP
Full cure and stoneskin, 5.28 HP/MP

High Quality WHM Cures
(811 power)

Cure 3, 306HP (107SS), 27 MP, 1.25s casting time
Full cure and no stoneskin, 11.33 HP/MP
Full cure and stoneskin, 15.96 HP/MP

Cure 4, 621HP (217SS), 49 MP, 1.25s casting time
Full cure and no stoneskin, 12.67 HP/MP
Full cure and stoneskin, 17.10 HP/MP

Cure 5, 1093HP(382SS), 68 MP, 1.25s casting time
Full cure and no stoneskin, 16.07 HP/MP
Full cure and stoneskin, 21.68 HP/MP

Cure 6, 1452HP(400SS), 155 MP, 1.25s casting time
Full cure and no stoneskin, 9.37 HP/MP
Full cure and stoneskin, 11.94 HP/MP

With 'gear' for Regen being Cleric's Briault and Orison Mitts +2.
'Low Quality WHM' for cures being Nobles body, Light Staff, AF3+1 head = 27% Potency
'High Quality WHM', /sch +49%pot, capped skill+merits, Orison Bliaud +2, Orison Pantaloons +2, +70MND gear




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I hate math and TL;DR:

If you're a junk WHM;

Regen4(merits) 8.53
Cure5 (SS) 8.19
Regen3(merits) 7.81
Cure4 (SS) 7.78
Cure3 (SS) 7.39
Regen4 (no merits) 7.31
Cure5 (noSS) 6.55
Regen3 (no merits) 6.25
Cure4 (noSS) 5.77
Cure3 (noSS) 5.47
Cure6 (SS) 5.28
Cure6 (noSS) 4.83

If you're a pro WHM;

Cure5 (SS) 21.68
Cure4 (SS) 17.10
Cure5 (no SS) 16.07
Cure3 (SS) 15.96
Cure4 (no SS) 12.67
Regen 4 (merits) 11.98
Cure6 (SS) 11.94
Cure3 (no SS) 11.33
Regen 3 (merits) 10.93
Regen 4 (no merits) 10.06
Cure6 (no SS) 9.37
Regen 3 (no merits) 8.98