Constant interrupts or Skills that specifically interrupt?

[CeveArthu]

Ruin isnt instant, Its not hard for a white mage to keep you constantly heavied, stunned, knocked back away from where you were running

Also why on earth would a chasing whm not use cleric stance?

[Gor]

Ruin isnt instant

Ruin isn't but Ruin II is. They're essentially the same thing just Ruin is a cast, has a potency of 80 and does not have an additional debuff effect. Ruin II is instant cast, does the same potency of 80 but gives the additional debuff of blind.
There is nothing a SCH can do to put Heavy on players. If you are getting hit by Ruin and getting heavied, that is because you are mounted of which any dd while mounted will give you heavy