Just from my experience with reaper, firebrand (condi/hybrid), and weaver they would be far too strong. Reaper would be able to take spite, blood, SR and reaper which is sustain (not as good without well trait) on top of beeg damage. Weaver yould be able to take fire, weaver, Arcane and any of the other 3 for bigger damage or sustain (and hybrid fire weaver needs neither of those things). Lastly, Imagine the standard burn guard, with all of the added bonuses that firebrand gives, like axe, quickness etc.