The reason healing stream is on such a low CD is because it is a huge part of their healing. Shamans are balanced around it. Being able to simply do 1 instant for 5 damage each 30 seconds would put the class in the gutter. Smart healing (especially when placed behind LoS) is never fun, but really if you just spent a little effort you could always have an instant for it. It's 3v3 not 1vs1.
What i'm saying is, it's wrong for a totem to even do anywhere near that amount of healing on such a low cd and being unable to kill it on top of that. Rshamans should've never been balanced like that and it's retarded that they are. And that number, you know, is actually really close to the real number (PvE-wise at least, PvP is probably the same).