If Aokiji’s on Marijoa, he can handle Akainu no problem. Kizaru might jump in, but his light would just get swallowed by the Black Hole.
Now, if Blackbeard snagged one last fruit, it’d be Kizaru’s. That combo of insane defense and speed? He’d need the extra mobility to dodge attacks, especially since the Dark-Dark Fruit already leaves him vulnerable. Pair the speed of light with Whitebeard’s quake powers, and he’d easily outclass Luffy. Plus, it fits, Blackbeard looks slow, and Luffy’s already keeping up with Kizaru.
As for Kizaru, he’s lost his purpose. Either he’ll fall to Blackbeard or he’ll join any pirate crew to fight the government, no way he can live with what he did to Vegapunk.