Is that so aberrant that different jobs have different play style with both strengths and weaknesses ?

Malefic II VS Stone III ? +10 potency for stone.
20% chance free dispell , 15% free Cure II , 20% that Medica cost half MP.
5y more range for Medica II than Aspected Helios
and so on.

And I don't even talk about 4 free heals (Benediction, Asylum, azzize(+MP and dmg), Tetragrammaton) Vs 2 ( Essential Dignity, and Collective Unconscious but you can't move )

3 Healers in the game,
all 3 are powerfull and unique.
WHM got most powerfull heals (single and group), and more healing skills and burst DPS
SCH got shields, fairy with micro management, mobility tanks to Dots and great MP effiency.
AST can be replacement for both, but slightly weaker for specialty, and cards.