What is the difference between MP regen and resting in FFXI. I like that I don't have to kneel to restore mp.

I don't think you've ever been in an NM fight then. I throw out heals to damage my hp so I can Shadowsear. Then Siphon TP to use Flashfreeze, then Siphon Mp to regain some lost MP. Sometime though rarely I use tranquility/exaltation. So the usefulness is still there.

And what does it matter if we spam DD, or heals? Melee spam attacks all the time. If we die it's our faults for not learning to make sure we don't die.