1. Luffy ain't invalid. Drums are kicking in soon to "Free" Bonney.
2. Kizaru couldn't do shit to Luffy but stall. Kizaru also is functionally in a coma and paralysed by his own words, even stating he ain't getting back up anytime soon. But Bonneys very soon dead and his crew has been frozen. And Oda ain't killing Bonney. Which means the drums are kicking in sooner then Kizaru recovers, Luffy will "free" Bonney and fight Saturn. Kizaru will probs get ups later, just in time for Zoro to beat Lucci and get together with the others to deal with Kizaru.
In either case this is blatant foreshadowing that the next fight Luffys is gonna have is against Saturn.