Rand comes into his own and is suddenly actually IN the fight as opposed to being a bystander. Aginor and Balthamel dying was relatively unimportant IMO, but to Sidious point, they gain confidence from realizing for the first time that the Forsaken were not actually that much more powerful than they are ... Moiraine was able to stand up to Aginor with her angreal after all ... Sure it was short lived, but it gave her a measuring stick that was not merely myth.

But to your point, the Bowl as well as a variety of other events could have been worse for the Shadow ...