I don't have my SCH at 50 yet, and don't have a matching relic weapon to get more precise numbers. When I wrote that, the Aetherflow gave exactly 600MP from 3003MP total and the Energy drains's gave something like 216MP, and gave the same numbers regardless of cleric stance.
Here's what I have currently on 3113MP:

So that recovered 1306, 622+228+228+228. That's 42% of your MP you can recover in less than 10 seconds. 3 seconds per recast on the Energy drain, 60 seconds on the Aetherflow.
Now If I switch to WHM (4353MP):

After trying to make MP hit zero by spamming Holy and Aero. 1584mp after Shroud of Saints finished ticking, So roughly 105MP/sec since Shroud only lasts for 15 seconds. That's 36%. Since it has a 120 second Cooldown, a SCH would have recovered 84% of their MP without even counting the natural regeneration rate in the same time it would take the WHM to recover 72%. But also nobody stands around for 1-2 minutes just waiting for MP to regenerate unless they were recently revived.
As stated It's not an apples and oranges comparison.