I am a little late in making this newspost as we downed this boss on the 29th. We even got fairly close on the Fish the same night, but lacked the time for more than 3 attempts. Radiance was mostly a matter of interrupting the adds, making sure everyone dodged tornadoes and deciding between a more tighly stacked or losely spread approach to that. In the end we went for more of a spread and letting everyone just handle it in the way they preferred and that did the trick for us. Well done everyone on the kill!
Link to logs