Obsidian mind makes it so that the super -no matter which one- grows faster. Yeah it doesn't gain on killing with the super but that's the only part that is lost. Let's say I'm in a nightfall and I'm running this. It just makes my revive that much more frequent. If I wanted to use it more often to become a flaming tank of bombing justice, I could too. It's amazing on voidwalker and very good on sunsinger.