The nerf of flare will be mainly noticed in dungeons, in for example FCOB you dont really get to flare more then 2-3 targets at the same time, i can only think of 2 instances.
The first week(s) in t12 where you had 5 bennus in the add phase and twin+gust+blood/sin combo in the add phase in t13 other than that it was normally just 2 targets. (not counting speedkill strat in t10)
So for raiding purposes this will probably not be a big deal.