The purpose behind for Ay is for balancing that's what Daiske said. I don't think her sb is meta breaking compared to Ay/Kakuzu/deidara (you can make an argument about this one).

This is a guess but I can see why they did that due to roshi teams and how good killer bee as a support during that time the instances were introduced. If true, same logic behind balancing applies here even though those teams eventually die from meta.