I'm sorry @White Flame but that is absolute nonsense. Plarium's (and any other game developer) default is to fall back on and blame RNG.
RNG is only as good as the algorithms that determine the possible outcomes, which are in turn determined by the developer.
Without any doubt at all, there has been a fundamental shift in Clan Boss rewards to XP Brews since the update on November 18th, and any suggestion nothing has been changed is an outright lie.
My clan are seething because of it, and several on the verge of quitting. If Plarium wants to retain any of the player base that still remains (after so many examples of incompetence) then I suggest it addresses this and not brush it off as acceptable.
CB drops aside, XP brews do not constitute a reward for anything, unless you're a very new player! It's bad enough that, as a 2 year player, they are so prevalent in Dungeons as rewards, never mind now CB NM & UNM. Ultimately they represent a punishment or booby prize, not a reward. There is a history of Plarium over valuing certain items (especially shards) within Raid.
This has successfully achieved one thing though, it's has successfully converted me from a player happy to buy a couple of packs per week to now entirely F2P, so congratulations on that. I will not continue to spend my hard earned cash on a product that then invests it in 'developments' such as the laborious Tag Team Arena then continues to try and rip its community off.
If I were employed by Plarium, I would actively encourage them to listen to the feedback on this subject.