As the OP example of HM EC, I love healing the Kephess fight with shadow tanks. I can pretty much set back and relax as a healer on this fight with two well played Shadows. Not difficult with a vanguard or guardian either, but with a shadow, I have no worries.
What is your Shadow Tank doing differently, then?
The way it was explained to me was that Shadows compensate their lower (even with Combat Technique) armor with the increased shield chance granted by Kinetic barrier. In encounters where those charges are eaten up too quickly though (basically any boss that has frequent hitting melee attacks, like EC Kephess and supposedly Zorn) that defense crumbles, and the Shadow is at a severe disadvatage compared to the other tanks. What am I missing?
Also, on another note, what is the official word on the 2.0 changes? I have read the patch notes, but of course I am not sure I evaluated them correctly. The way I understood for example the Shadow changes was that it's mitigation actually got worse (the 20% armor buff is removed, and Kinetic Barrier got a longer cooldown), but in turn she got other gimmicks like increase to the healing recieved and an encounter specific way to buff the healing output in general. Which seems to put the Shadow even further into the 'tricky and gimmicky' direction compared to the 'I just shrug it off' attitude of Guardian and Vanguard.