End game lesson learned based on me playing both SCH and WHM with i90 t5 kill experience:
You need WHM+SCH combo. SCH excels in some areas and WHM in others. Main things SCH brings is Burst heals and shields. Main things WHM brings is AOE heals, stoneskin, regen, and oh shit benediction.
Can you run 2x WHM sure. can you run 2x SCH? sure. but nothing beats WHM + SCH. The utility they have together in all situations is vast.