I see it like this:
Yes, you're the Dungeon Lord. But classically, in dungeon adventure games or roleplaying games, that's what heroes do. They rape and pillage dungeons. They walk into a rat's nest, kick the mother rat in the face, stomp on her babies, set fire to the nest, then bitch about the xp and the diseases they just got.
Truly villainous bad guys like heroes to be at the top of their game when they chop them down, just to let them know they had no real chance in the first place. So letting heroes get full of adventure and loot, then killing them and harvesting them for twice the soul energy, that sounds devious to me and like it could support a lot of tactical and building decisions in the actual game. Like how best to get them as full as possible, then in a position to get killed before they can leave. I'm glad they're not just going to plow into the heart of your dungeon.
So Realmforge is trying to do something like a dungeon life sim. I'm digging it. It's what I wanted DK to be but it wasn't. On the one hand, I'm thinking the life sim on YOUR end won't be the same. I'm taking a wild guess that you place monster generators and they puke out monsters when heroes get near. If you want them for defense, you build three monster generators (or lairs). I'm guessing you don't have to feed or keep your minions happy, or any of that.
So basically they've taken DKII's model and flipped it, while still keeping you as the Dungeon controller. Soul Energy is what they use to justify it, and they're attaching a bunch of stuff to soul energy so you have a reason for wanting to keep them happy.
I think it works, at least as they describe it. I'm hoping these "torches, skeletons and lanterns" turn out to be semi-interesting. If it's just ever more expensive visual items that bump up hero happiness or whatever...that might get a little boring. It would be nicer if they did something beyond just looking pretty and juicing up heros.