Well, those are very extreme examples of like M+20 to 25. Not many people in general are doing that.
If you look at M+15 in wowlogs :
https://www.warcraftlogs.com/statist...=15&metric=hps
You will see that druid is top tier, mid tier is hpally, rshaman, and hpriest. And low tier is disc and mw monk. The number of parses, as well as healing, of pally, shaman, and holy priest are all pretty close to each other so I think they seem pretty solid. Shaman also has lots of utility so its a great option for M+. I'm not sure if we need any major buffs or anything in that case. I will agree with others that our defensives are low.... more baseline HP or damage reduction would be good, Shaman has always had low HP and with how high the damage is in higher M+ it can lead to being two shot basically without much we can do about it. Also, we only have one personal defensive CD and no tank CD (unless u count SLT) so limited options to counter big abilities... but again, we got lots of other utility including interrupt and purge so maybe they have made us weak on defenses on purpose.