BB isn't a DoT though. It's damage is determined by how well you know the spells radius and knowing how to kite it in and out of that radius efficiently.
In most cases BB, doesn't work to efficiently on ranged mobs(casters, archers) so its only useful for melee units. Nerfing BB to 30 secs wont be to bad (but cast time better be changed and Cool down untouched as a result) as I say its how efficiently you can kite and will still be more efficient them most of you other spells. If they change the save or something else on BB then most Caster Clr/FvS just become healers with lots of wasted feats.