Just thought about something. We know that in the beast pirates a Tobi Roppo can become a calamity by earning the right to challenge one and then beat him so it would make sense that this works even for headliners with the Tobi roppo. Yet we have also the beast theme:
Kaido is a myth dragon zoan.
King is a pterodactyl, Queen a brachiosaur and Jack a mammoth (it exits a bit from the dino theme but I guess it still works for the ancient zoan general theme).
Innthe Tobi Roppos we have Ulti has a pachy, Drake has the allosaurus df, P1 the spunosaurus and most likely the other 3 have ancient zoans as well.
But these are all df hard as hell to find around. How is it that these people have all these rare ancient zoan df? Even worse conaidering that the recruits rarely will have a zoan and it is alnost impossible for them to have an ancient zoan (and Drake is the exception that confirms the rule) so, ingoring people who already have df (like Hawkins, Luffy, Kidd) how they manage to get these ancient zoan df?
It could be that the fight to rank up are actually death fights and in any case if the winner has no df then he must take the df of the loser (with the fruit method Jesus wanted to use on Luffy) and eat it. If he/she already has one then the fruit can be stored (or maybe it has not to be a death fight in that case but a death fight just works perfectly for the beast pirates). The problem is people who already has another kind of df (like Luffy, Hawkins etc.) maybe these guys are simply forbidden to challenge higher ranking beast pirates to increase their rank and their limit is the headliner one. This is also reinforced by Kaido obsession for zoan dfs, he even wanted to make a full crew of zoans by using the smiles (and this ended with the grotesque low rank beast pirates we have seen so far).