Ignoring the t8 bonus, spamming lb is still going to be the way to raid heal consistent damage(in between WG cds of course). I found this to be the best course of action for Stormbreakers Aura/Hodir's Frozen Blows. And on predictable raid damage like frozen blows, I found myself getting a 2 stack of blooms on as many people as possible beforehand. It really was quite effective, the added power of blooms is nothing to sneeze at. Without crits, it's pretty much an on-demand 6k heal to as many as 7-10 people. Which to me outways possibly being ready with a swiftmend.
Of course, once the T8 4pc is factored in... I have no doubt this will become obsolete as spamming rejuv's is going to be incredible. Though a mix of pre-blooming before the damage + rejuving while its occuring will probably be most effective.
Whatever you are smoking, I want some.
My guild is all the way up to Yoggy and Spamming LB is NOT the way to raid heal anymore. It just doesn't work well. Using Rejuv (even without the t8.5 set bonus), regrowth, and the occasional Nourish to top them off works much better. Mana efficiency plays a big roll in the major fights in Ulduar now, and LB stacking on multiple targets is no longer mana efficient. Stacking LB on a main tank, however, is still the best way to go.