Actually inverse shadow works for both classes so it does help you get radiance faster. Although the nova bomb ability goes to waste, yes. But I still find inverse shadow a very useful perk. The vault raid helmet had it white the ceota one does not so if you are looking to build a warlock that spams radiance the obsidian mind is the only helmet that can help to the same degree and still get you to level 32 that I'm currently aware of. That and the thing still looks pretty cool during radiance. It's literally a flaming helmet of darkness.