Plus, you still do a shit ton of raid healing in 10M. My healing partners are an hpal and holy/disc priest, and I find myself raid healing more than tank healing.
From a 25 man raiding perspective, I think that both our 2 piece and 4 piece are pretty terrible.
2 piece - Even with the T14 2pc, it's debatable whether Greater Healing Wave is worth using over Healing Surge. With or without the bonus, Healing Surge is slightly more HPS and GHW is slightly more HPM. In a 25 man raid, shaman are normally not primarily assigned to tank healing, making GHW more of a spot heal on low health tanks/raid members. On the majority of fights, you just don't use it enough to get a lot of value from the mana cost reduction.
4 piece in 5.0 - Nearly completely worthless. I find it very rare that I want to cast 3 consecutive single target heals. Casting 3 in a row is the only case where having a third charge of Tidal Waves benefits you, because Riptide will be back off CD after 2 GHW/HW casts anyway. Without Riptide glyphed, I generally have 90-100% Tidal Waves uptime, meaning that the set bonus at best gives 10% more uptime. I just don't see a practical purpose. Even if you are dedicated tank healing for some reason, you will be weaving in Riptide enough that you don't often want that third charge. The one use I could see for the set bonus is for Tsulong. The 3rd TW charge would allow you to cast 3 straight TW buffed Healing Surges during the Sun Breath buff.
4 piece in 5.1 - I still see it as marginal at best. Again, I don't think you cast enough HW, HS and GHW, and HW and GHW with TW up are already faster than the equivalent spells that other classes have. It's still going to be a very underwhelming set bonus.
To say it's the best of all the healers is just ignorant. In particular, the holy paladin 4 piece is amazing, effectively increasing their holy power generation by about 35%
I share tier with the two Warrior tanks. Needless to say, it was an easy decision to pass it to them.