User blog comment:Crimson and Darkness/Shin DxD 3 discussion/@comment-105.226.163.238-20190808074119/@comment-36523287-20190808080246

Ishibumi have held Issei's growth back for some time. So, his friends could kept up with him. Since he will not face any of his friends in the tournament anymore, the authur might feel OK to finally give Issei new powerup. If Issei got AxA too soon. he would basically could steamrolled Rias and Kiba which wasn't Ishibumi's writing style (He rarely let Issei simply overwhelm opponents)