Issue 1
Shaman has poor AP management skills making it inferior to other healer classes.
Why is this an issue?
Shaman has two tools to manage own AP: Restorative Burst tactic and Yer Not So Bad AP drain.
In the current disrupt meta the AP drain gets disrupted too often to be reliable and so fails to serve its purpose. When facing premade groups it's often necessary (depending on the quality of enemy healers) to cover the AP drain with another dot to make it harder for enemy healers to cleanse the AP drain. If your cover dot gets disrupted you have to either keep trying to cover or drain anyway and risk it getting cleansed. Either way you will most likely burn more AP than get back from the drain. This means that at high level play Shamans AP issues get even worse.
Tweaking Yer Not So Bad is impossible without looking at disrupt rates as a whole which is a separate discussion so if we want to address Shamans AP issues specifically we have to look at Restorative Burst.
At the moment Shaman has three ways to proc Restorative Burst on RoR: Gather Round (2.5s 65AP g-heal), Bigger, Better An' Greener (2s cast 45AP st-heal) and Gork'll Fix It (1s cast 55AP st-heal). Gather Round is too slow and expensive to serve as a way to bounce back from a AP deficit. Bigger, Better An' Greener is both slow to cast and also less likely to proc RB since it's a single target heal. Gork'll Fix It is insanely expensive. In stressful situations all three fall short in helping you to proc RB forcing you to rely on double AP pots in order to function - a situation which no other healer has to face.
Solution proposal
Make Do Sumfin Useful ticks count as direct healing like it did on live.
How do you know that this is how it worked on live?
Exhibit A: https://www.youtube.com/watch?v=az8HWo9 ... u.be&t=203
Around 3:26 mark WSCT shows Do Sumfin Useful critting for 738 hp and Restorative Burst proccing at the same time.
Click here to watch on YouTube
Do Sumfin Useful is specced and Restorative Burst is slotted:

Exhibit B: https://www.youtube.com/watch?v=mxGqw32 ... tu.be&t=33
Around 0:33 mark WSCT shows a Restorative Burst proc with no castbar
Click here to watch on YouTube
Do Sumfin Useful is specced and Restorative Burst is slotted:

Issue 2
Shrug It Off doesn't stack with tactics like Blessing of Chaos and Transferred Focus.
Why is this an issue?
Lack of synergy with other classes makes Shaman a less desirable pick. It is worth noting that Archmages Magical Infusion does stack with Runepriests Blessing of Gringni. A ticket for this issue with clear evidence has been open since March 2017 with no direct acknowledgement. In the past when it came to stacking rules the team took clear stances on what's acceptable (Wrist Slash) and what is not (Hastened Doom). It would be nice to get a confirmation and perhaps a fix for this issue in the near future.
Solution proposal
Make Shrug It Off stack with tactics that increase incoming healing.