That was my first thought - if the shaman was keeping their assigned groups/players alive and other healers weren't having to cover for them the officer who wrote in was offbase in suggesting performance ideas. Some people know what they need to do to do their role and, especially on farm content, will not play optimally because they don't have to in order to do their job.

Healing and tanking is also harder to critique than DPS. If a tank holds aggro and is not extraordinarily hard to heal they're fine. If a healer's assignments stay alive, again, they're fine. DPS is easier to point out because you can see numbers - but even there it can be tricky. For example, my DPS on Lich King the other night was a bit low, but 1) I was using Mind Flay to snare the Valkyrs over and over (vs doing a max DPS rotation) and 2) I was on Ice Orb duty when those were out. So even DPS can be tricky - yes, my meters were low on that fight, but snaring Valks and helping to ensure that the grabbed player lived and Ice orbs didn't reach the raid was way more important than my meters.

Finally, the rogue example highlights the issue of standards. Yeah, the chart topping rogue might have been better than the one who wasn't putting up the same numbers even setting gear differences aside - but were bosses dying? Was the second rogue doing reasonable numbers for their gear level? IF so, realize that not everyone wants to spend hours perfecting rotations. In a server first guild, that's an issue perhaps... but in most guilds it's not.

Good point and similar to what I thought of immediately when I read the letter and article. Discussing technique is important, but First Things First! Start with setting definite standards for how much damage, how much threat, how much healing a player needs to generate, giving some specific examples using specific fights. Make the standards reasonable.

Having set standards, then, there's no need to wonder how to approach the subject with players who are clearly using some ineffective techniques (or gear/spec/gems/etc). Don't begin by talking about technique, just present (in the most constructive way you can muster) the difference between their output and the guild or raid group's expectations of them. Next, if they don't care they will leave or be asked kindly to leave. If they do care they will either do their own research and improvement (problem solved!) or ask for advice/suggestions/training (problem solved!).

healer meters?
/slash wrists
After a pug 25 my healing number was low. All my assigned players
stayed up, no one died, I kept them topped with appropriate HoTs..and
my healed & overhealed numbers were low. My reward? I got booted when
the group reformed to rerun as a 10 man.
My numbers were too low, ______ (you know who you are) had topped the
heal charts; not only overhealing his assignments but poaching heals
(unneeded) on mine. During the fights I was chuckling to myself,
watching his spam-a-thon. My thought was that a competent raid leader
would see this as well. Well...no.
"Thanks for the run, but we don't need you on the 10 man, _____'s
healing was over twice yours, you should get those healing numbers
up" When I whispered _____, he said, and I quote "Sorry dude, you
should do your best to top the meter every fight, every run, EVEN IF
YOU ARE OVERHEALING"
When I politely explained keeping them topped allows for less mana
use and more cushion in case of spike damage, he explained that he
let them drop in health so his heals were larger. WTF? A healer,
allowing his targets to drop in health, on purpose, so he could top
charts in effective healing?
*sigh*
When he went on to tell me that it guaranteed his slot when he could
post heal meters, he consistently topped healing charts, he ended up on
/ignore as I sat and shook my head.
Him: "Ok, doctor, let this patient's infection run rampant, hospitalize them, then through
heroic surgery and advanced medicine save his life!!!"
Me: "I'll wash the cut with soapy water, throw some antibiotic cream and a bandaid on it,
you're out the door...next in line please?"
Which doctor would YOU rather have in charge of your (virtual) life?

@Blacksen "If you asked them to heal group X, and they heal group X, then they're clearly playing up-to-par"

Thank you