Well, everyone with Yonko level ACoC is a Hakiman to some extent. Luffy has a Mythical God fruit, ACoC, FS, barrier Haki and internal destruction and he will probably beat Blackbeard by excelling in Haki even further. Meanwhile Kizaru has a strong logia with puny Haki. Luffy having both superior Haki and a superior fruit, makes it hard for Kizaru-chin to compete.