Next time appear:
Katakuri 3.4 Billion
Sabo 3.5 Billion
Yamato 3.1 Billion
Doffy 2.7 Billion
Enel 3 Billion
Actually very good estimates. As soon as
Katakuri steps out of his mothers shadow his potential is huge. Same as Blackbeard, Big Mom or Whitebeard that all had 0-?? in bounty but none were yonko.
Sabo because of his strength, potential, connections, world fame and knowledge of Mariejois secrets is one of the most dangerous guys in the world.
Yamato is an unknown quantity but strength wise she didn't exactly seem scared of Green Bull. Luffy has secretly entrusted Wano to her. That alone speaks of her level. Also Kaidos daughter and oni blood.
Doflamingo is a more accomplished Crocodile who himself is 1.9. Add to that potential prison break, being a fallen tenryubito, Underworld connections, no longer scared of Kaido and knowledge of Mariejois secret and you have a very dangerous pirate.
Enel is an unknown quantity with the power of a God. By himself he can recreate the feats of the Mother Flame and his CoO is top tier. So basically he can target an island from the ocean or his flying ship and destroy the island with ease before they know what hit them.