OK, first of all, so that I don't get instantly shut down, I'm a Sunsinger, and I use either Song of Flame or Radiant Skin, depending on situation. However, I do this because I like grenades. I entirely understand plenty of reasons why someone would want to use Fireborn, and plenty are team related. One is that, in the case of a surprise party knockdown (think cursed thralls), they can salvage the whole strike or raid. Is rather handy. Second, they might be newer to a raid or strike, and not want to hinder the party as much. Third, they may like to be less of a burden on anyone in the case that they drop. And forth, some people just like having an "oh shit " button. Now, if they save their radiance for self rez, what is the part missing? A burst of dps every few minutes, yes, I'll admit that, assuming they go 'nade crazy. Possibly increasing the teams cool down with Song of Flame. However, this means they have to be close enough to effect someone. Not always feasible. Some short lived extra survivability, if they are using Radiant Skin and possibly Flame Shield. Maybe more if they are using Apeothesis Veil, but most Sunsingers seem to rock an exotic chest piece or gauntlets instead. This isn't really that big a trade of for someone who could possibly save a strike or raid. That said, team up with who makes you comfortable.