it makes perfect sense since his hollow powers only activate in hueco mundo so if he went back to earth he would suck again and be useless as a character. plus kubo made him be all evil and stuff in his past there has to be a reason for it. i believe that his hollow powers, being amplified on hueco mundo will begin rotting his mind and reverting him back to his bad old days, they will then grow and encompass his entire body in armor. he will become an evil hollow and fight the good guys, and finally kill one, in his first ever bleach victory.