In my experience at an advertising agency “Making people feel good” was the best result of brainstorming, but certainly not the only one. Everyone had a chance to voice their ideas and offer feedback on other ideas. In the end the ideas usually ended up coming from the people who were great at making ideas, and the tactical executions of those ideas came from the people who were good at making ideas come to life, and sometimes they combined to make an even better idea and execution.
As a creative leader I also required each person involved in the brainstorm to do individual work beforehand. Perhaps this is why we saw good results.
Either way, measuring brainstorming success by number of ideas or some other measure of “creativity” is likely missing out on the social benefits of the process.