Already have had a few encounters like that.
I just slide nearly everything to the right except the SoS heal and the ToL slider and then it's fine.
My realm and battlegroup is low pop on healers and tanks (nearly 24/7 bonus for those 2 roles in LFD).
So whatever is there, is very good (most on my realm can easily soloheal the 3rd boss in BH)
While I see my druid doing 10K HpS, others are pushing 20K+ and yes, then you get told for slacking.
And it's not the gear, nor enchants, talents or reforges.
I follow Noxxic.com pretty much for stats, and have a average iLevel of 384.
If I'm as you say in a poor group, or not all the healers are around yet and they pull trash, then the CC pushes much more HpS so I'm not blaming the CC for this occurence.