"Twin shield arts. That's the unique form of combat I will show you all. Especially since you can all wield shields and are not limited to just one."
The reason Su found herself in this odd situation wasn't just because of the growing number of people finding classes that were similar to the heroes that they adored. That was just a part of it.
Many people had begun to idolize the heroes along with the representatives on the Genesis council. That was to be expected. Those that decided to pursue Su's example were those that had seen her kindness and ability to defend those around her. They had witnessed it and been inspired.