Not sure how your trying to defend spriest off healing just because another spec is better, if spriests had the same off healing as S11 there would be no issue imo, Rets are balanced around huge off heals at a cost to damage, spriests were not intended to have these huge heals that make them able to take on the role of healer.
Spriests can literally babysit a team so hard with off heals + MD it is beyond a joke.