Raids are a problem in high tier gear. Delves are a problem in low tier gear. Because there are overlaps.
When tanks were inmortal there was no tank shortage. Tank shortage == longer quews. We want less quews.
When damage was not so bursty then healers were not so stressed. Healer shortage == longer quews. We want less quews.
Forget BL and BR. Those are inconsequential.
Stacking raid buffs implies 10% (or more) performance. And some of those buffs are so unique they should be given equivalent performance to all other specs.
For example: Chaos Brand from DH AND mistic touch from monks should BOTH give 3% Damage. Not specifically magical/phisical.
For example: Mages and Warriors should BOTH give 3% main stat. Not just Intelect/AP.
For example: PI should be turned to BL. Or BL to PI.
For example: MS and gate should be turned into a Shroud. And vice-versa.
Things like that…
Works fine on what? LFR level of difficulty? Normal Dungeons? 
Go ahead… knock yourself out. You got 3000+ posts to read.