It depends on your definition of easy. As a sch i need to push more buttons. In that sense whm is easier. Less choices, less buttons. Less buttons also means less control however. Less actions per gcd.

So overall I think sch is easier if you can handle buttons. Pet management is easy, macros make it easier, mana is a joke to manage and having lustrate means you can respond to things much faster. On a single target there is no question sch is easier to keep a tank up with. Aoe is a little more complicated on a sch but just because a whm CAN spam aoe heals doesn't mean its easy, you'll destroy your mana and generate threat.

Both healers must be proactive, just differently.

The Sch version of proactive is preshield, mitigation, and if somehow the tank still gets hit too hard they have lustrate.

Whm proactive is timing heals to land as or right after damage lands, that means you need to understand the fight enough to start casts before scripted moves and understand autoattack timers. Tank gets a bad hit, hope your tank doesn't die in the next gcd.