Your druid/shammy example makes sense in that the druid would build threat quicker; however, I'd stray away from using the words damage and threat interchangeably due to threat modifiers. As I'm sure you've seen, dps gernally out damages tanks by a large margin yet fall behind in threat production. The point I think Fursphere is trying to make is that with straight out spam by a boomkin, their threat modifiers aren't sufficient enough whereas a shamans generally are.

As for the castsequence blanks, I know, I was just kidding.

Edit: got interrupted while typing this and Fursphere beat me to the reply.