When Axel shows up in KHII in Betwixt and Between, he's already pretty beat up and weak. The manga just explains that Saix did it. Like how the novels showed the scene where Roxas and Axel talked on the Clock Tower after the Sora fight and the scene where Roxas got his name before KHFM did it. Is it good storytelling? No. Is a it a thing? Yeah, kinda.