Err, I honestly can't say if its better or not. I know its been changed and due to me so that always messes up how I view things.
I agree that Luna getting corrupted by an outside source always seemed a little cheap to me. However watching Luna slowly go crazy as other ponies continually ignore her could be interesting if heartbreaking.
Well that was awesome
I guess my headcanon with Luna's corruption into Nightmare Moon was just frustration and jealousy. Kinda. She went into the plan willingly but progressively became more and more insane. Celestia failed to talk her down because Luna's hate was focused a lot on Celestia and her day. Ponies called her a monster so that's what she became in response.
As for the elements the reason for the variance goes like this in my head cannon. Celestia and Luna using them have less effectiveness then the Mane 6, the other reason for the variance is due to possibilties. Discord can only ever be sealed away and turning him to stone is the most effective method. Nightmare Moon was too powerful and too hateful to initially be anything but sealed away but was sent to the moon instead as a weaker seal that let her think. The second time the Elements were more powerful and Nightmare Moon had calmed down over the last thousand years so they were more effective and could purify her.