Then they don't know what they're talking about, because we can't actually target that many people in a ten second window. Wild Growth once (which you would have cast anyway), Efflorescence once (which doesn't really help unless you already had to recast it), and then a couple of Rejuvenations or Regrowths. That's very underwhelming.
BL lasts a fairly long time, so he could still get it ~30 seconds into the fight. Then everyone else can hold back a little and conserve mana. There are also several fights with a burn phase at the end that you want to save Bloodlust for: Ursoc, Cenarius, Xavius, and of course Il'gynoth. On all of those fights, innervating the shaman would have made sense.