Step out of Abyssea and see how long a 61 WHM can hold over RDM in endgame situations. This isn't much different than people saying anyone who subs WHM is as good a healer, as RDM's healing isn't all about raw curative power, but how Fast Cast helps them get cures out faster while debuffs keep damage from coming less often. A 61 WHM will not be landing Slow or Paralyze, nor have anywhere near the MP longevity or potential cure potency.