Legends of the Sword coast doesn't have a good DM mode worth emulating. It is a bizarre annoying thing that isn't conducive to a fun PnP style experience.
NWN however does.

A DM mode isn't the place for a bizarre competitive round robin mode, it should be attempting to emulate table top as much as possible, and through that desire the DM should have as much power and ability to change things as possible, the more editor functions they have access to in game (not to mention console commands) the better it will be.

"But Raith, building a big detailed area in game would be time consuming, what about that?"
That's why you should be prepared and have the major areas built if not populated in the editor before even loading it up for your group little one. Simple, no?

"But a DM should have a skill tree and gain levels and stuff to get more crap to do in the game!"
Why? The DM isn't in competition with the players, he is facilitating their story and game, now if this story kills them oh well but that isn't a success for the DM, it is simply the way it played out.

But if the DM can do anything from the start, what's to stop him from winning?
...The DM isn't in competition with the players, and if you have a DM (or you are that DM) that think that killing the party is "winning" then you shouldn't play with him/shouldn't be DM.

"DMs should be able to control the monsters directly to fight the party!"
I'm not against this, but it shouldn't be mandatory because personally I would be using that time gained in battle setting up the next area if it needed it.