Anyone who insists Kaido's title is just make-believe and that he's actually a fraud needs to provide proof of whichever other top-tier being stronger. Kaido has 60+ chapters worth of fighting an entire gauntlet while holding up an island, not to mention the several claims from multiple characters stating that he's the strongest.
What do other top-tiers - besides G5 Luffy - have to compare right now? For instance, Shanks one-shotting Kid and Killer is definitely impressive, but AP isn't the sole determining factor in who wins a fight.