It's not about being edgy, it's a matter of "Look at the title of this fucking quest, if we don't take the initiative, events will almost certainly conspire to force us into it."
And frankly, the idea of being a nice, cute, affectionate blonde who happens to be the Overlord amuses me, especially if we don't go and use that as an excuse to be a horrible monster, but instead to just be a cute and affectionate ruler of all demonkind.
That being said, Uniques are almost certainly something we can only get through evolution perks, and I'm not keen on spending our "Free level up and XP boost" while evolving is still relatively easy.
Consider, for instance, the likelihood of demons being used as a cats paw to do things, summoned or otherwise directed here to cause tragedy. Mark of the Demon King means that we can tell them to fuck off because this is where we keep our stuff, and that will probably take precedence over any lesser orders.