I'm still a huge noob, but I don't know if I would agree with that being a reason to keep hitting the Dark Lord. In my limited experience you want to hit and take on the highest level mission leader you can. You get XP for attacking them over the easier leader, get better drops (in my experience), and have access to their girls if you don't have them yet. I know there are ways to use your level 1 girls with the right gear to possibly get XP from those lower level leaders but guess I rather just attack the leaders I need the girls from or the one that matches my current level. But that is just my opinion and don't agree with your statement.