For me it's simple what makes a good editor.
https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSo56yAlA8SXRk9sIp6OarNnsoVjR5_dkr9rgoxUG_571bVUfOQfw
If I can't make this simple layout in less then a day. I mean layout not making it look pretty with props and atmosphere lightning, sounds etc ... Then the editor has failed. I realize NWN1 was tile based and so was NWN2 dungeon editor, but that shouldn't be an excuse.
It shoudln't take you more than a few hours to do the layout for a HUGE level. If it takes you longer, you just need more practice.