My theory. With a 1sec GCD, lifebloom and rejuvination spam are very effective methods of healing, providing extremely high mana efficiency and easing the burden on other healers. While Wild Growth is an effective spell, I believe that the 12% intelect -> SP is worth it.
As I get more haste, I can drop more from GotE to get more points in Living Seed. As it stands haste is second only to spellpower.
Alternate, shift Living seed up to Nature's Bounty, or move Improved Tranquility to another location. (I use Tranquility on pulls like Auriaya where severe burst is extremely likely)
I tested this during 10man Ulduar, and on Mimiron, Thorim, Council, and Freya it seemed no less effective than with Wild Growth. I have 2800-2900 Bonus Healing raid buffed.
Eh, no matter how fast you are, you won't be able to beat a WG on 5-6 targets. Sure getting roughly another 100 or so SP is nice, but that won't make up the fact that you have to spend more GCDs trying to raid heal. Also if you do MT heal more, you are missing points in Living Seed and Gift ot Earthmother which is pretty important in my eyes for putting out fast heals. But I'm sure this build could work.
With WoA totem, plus my celestial focus, I only need 544 haste to have 1sec GCD with 3/5 GotE, so the missing points there don't impact my healing. I have never been a fan of Regrowth (the direct healing part), Nourish, or Healing Touch, they heal for very little compared to the time spent casting, relative to lifebloom and rejuv. Most of the time I am given the job of healing two or three tanks at the same time, and dropping some raid heals while I am at it.
Lacking WG is a blow, and one I believe that few people will try.
Why? WG is amazing for raid healing on every encounter. Healing touch sucks sure, it's only use is to NS it. Regrowth I don't really use much except as an extra hot to help extra tank damage. Nourish I didn't think I would like but it's insanely useful and if you glyph for it it's a very strong and efficient heal. It's an interesting build I guess but 100 spellpower isn't a huge deal, and it's imo pretty dumb to give up a great raid heal for it. And living seed with Natural Perfection is also pretty helpful for tank healing.
Basically it seems you've gimped your healing tools for 100 more spellpower. If you aren't using regrowth at least situationally and nourish you're not doing what you should be.