That's kinda like saying "Akainu didn't kill Ace he just put a permanent end to his bodily functions"
BB cheats but it only affects the powerscale. It's fair game within the story. There's no such thing as cheating in a pirate fight. I'm just saying he'll kill Shanks in a way that'd still allow for Shanks fans to say he wasn't stronger. Which Oda does on purpose to keep y'all hooked