Needing to apply 2 dots and then Bane to spread it when WHM/AST can just Holy/Gravity in one GCD is one of the main things that put me off SCH/SMN for years. But I do agree there needs to be something more interesting.

Whether or not that needs to be via AoE damage.
For single target, it bugs me that Ruin II is basically useless outside of movement. Not sure a Healer really needs that sort of utility, more of a DPS thing, so a hangover from ACN.
Would be nice if Ruin II could be upgraded into something that would interact with either Broil and/or Art of War.

But I would most like to see both Art of War and Gravity gain some sort of crowd control like Holy.
Stun is probably the most effective form right now (and most disruptive in pulls) so I wouldn't expect it to be that much.
Ideally Gravity should gain a Slow debuff for maybe 6s, and Art of War could be improved if it came with a a damage down debuff and a DoT.
If Art of War was say a 6s Reprisal debuff with a 6s DoT, so three ticks of damage, and then Ruin II had some sort of interaction, then it would be viable to alternate them.