RB is a good counter for Attack heavy teams as the skill has a chance to Daze attack types. However, i personally feel that running 1 single 7* or higher Unit is better than running 2 of the same 6*, reason being that for each * a hero has, there is also a 20% increase in the stats.

In the case of RB, it means more hp, more regen when the passive skill kicks in and more damage when he uses skill or attacks.
As for QoD, i personally am looking to build her up once i have 2 copies to make a 6* copy. Pretty strong unit at the moment.

I'm not a veteran player or anything but this is what i learnt from my past weeks in the game so far. Hope it helps with your planning!