Well, Syphon Strike alone already refunds like 90% of the amount of MP you used for DA if you add another MP over time refresh, you'll never go into "mana drain when spammed" if you just repeats the whole 3 GCDs combo.

And Having a move that damages yourself as a tank makes the healer's job more difficult. It's already bad enough with STR tanks on DPS Stance main tanking, now they need to deal with STR Tanks on DPS Stance taking 10% damage every 10 seconds? That's just terrible.