SCH is much easier to play than WHM - much less mana issues to worry about, much less aggro to worry about, much less damage to heal due to the shields. Plus when you go Cleric Stance, your fairy and Lustrates aren't affected and Eos/Selene keeps on healing leaving you MORE time to be in cleric and DPSing. WHM, not so much. You have no fairy to help you out, no Aetherflow mana regen every minute, no three Lustrates per minute, etc.
I was thinking more along the lines of: are both SP and SE up at all times without being replaced early (they give enough leniency for one Wrath move and one Fracture during constant uptime) except to make sure SE buy FFXIV gil (and Berserk, if possible) are up for Inner Beast? If he needs additional threat via Butcher's combo, is it being placed ideally? Is the War using Berserk to complete his 5-stack when spending it on anything but Unchained? If in Defiance, is (Unchained)-Berserk after pull starting on the third combo move, as to allow for a combo-end, a combo, a wrath move, and another full combo in your 9-hit Berserk? Does he have enough skill speed to do a 9-hit Berserk? Where it does not generate excess/unusable Wrath and you have no particular need for them, are you avoiding Steel Cyclone/Inner Beast during Unchained? Etc.
If played to absolute theoretical perfection* (which falling behind dps in gear may not allow anyways), the only classes that can give me similar difficulty are certain skill-speed levels of Monk and Ninja. If played just 'damn well', then it's a bit easier.
As for the above comment on Black Mage, it is easy in terms of mechanics, but if one considers 'mastery' of the class to arrive only after you're parsing as high as possible, it's actually a fairly demanding job.