Also, casters are ruthlessly punished by mechanics. That's why their average damage per hit is higher than the average damage per hit for melee classes. This is by design by the game developers. Just look at the potency values and you'll see. Fine, not convinced?

Let's say I'm playing a BLM. I'm doing my rotation. Uh oh. Titan put down a knock you off the platform right under me. Lets tally:
Interrupted cast: 1.5s
Moving: 2s
Moving back: 2s (yes we do this too, mechanics)
Hard cast B3: 3.5
9s of no dps

Now I probably lost Astral Fire which means I lost Enocian which means I lost progress for Foul.

This would be akin to SAM losing all their Sen and Kenki.
Akin to MNK losing greased lightning.
Akin to NIN losing Huton and putting Ninjustsu on CD.
Akin to DRG losing BotD.