Is mp5 irrelevant on progression fights?

I've run into some very strange gearing issues lately. The main problem for me is that the value of mp5 fluctuates wildly from fight to fight. The main reason is that for most of the progression fights, there is either so much raid damage that our Water Shield makes gearing for mp5 on these fights completely inefficient (Putricide, Blood Queen, Sindragosa), or there are mechanics that make mp5 irrelevant (Valithria).

To give you an idea, Water Shield procs every 2 seconds on Blood Queen, which combined with Improved Water Shield gave me about 540 mp5. On Sindragosa, Frost Aura causes Water Shield to proc every 3 seconds, and combined with the forced throttling of Unchained Magic, I never need my mana tide on either of these fights unless I die unexpectedly. Some shaman will carry multiple sets for different fights, and for these fights would opt out of mp5 entirely; I'm too lazy to gem and balance multiple sets myself, but I have to figure that if I'm going to min-max for any fight, it should be the hard progression fights, right?

In my combat log parse last night, my Insightful Earthsiege Diamond got a distressingly low HEP value of about 40 HEP. While most shaman agree that The Revitalizing Skyflare Diamond is the best choice when you have double solace, I'm thinking of switching to this even though I don't even have those. In addition to gaining the crit heal effect, I will be gaining a little haste by replacing the one mp5 gem I have to meet my blue gem requirement with a yellow haste gem.

So I think I'm going to start moving away from mp5 entirely, starting with my meta gem, and then replacing my boot enchant with Tuskarr's Vitality (which I should have done a long time ago). I'm hoping it's not going to be super painful when my guild gets to heroic modes, for fights that won't have these contstant damage mechanics, but I guess we'll see.