1- Shimotsuki Ryuma (Stated in Wanted! Monsters like "the strongest in the world" in his time and as I believe he is from the Void Century, therefore he would be the strongest.)

2- Imu (somehow surpassed Joy Boy, but lost wars against Wano🤭. Imu also nullified Sabo's attack and ignored its durability.)

3- Joy Boy

4- Rocks D. Xebec (Roger's Strongest Rival. > Whitebeard)

5- Edward Newgate (Strongest Man in the World in his time)

6- Gol D. Roger

7- Shiki (One of Gol D. Roger's biggest rivals.)

8- Monkey D. Garp

9- Sengoku

10- Dracule Mihawk (The strongest swordsman of his time, together with Shanks, form the strongest rival duo today. He was called the World's Strongest just like Ryuma after Whitebeard's death in One Piece Green: Secret Pieces).

11- Akainu (Scales above Shanks' Kamusari that knocked Kid out. His MEIGO technique would kill Kid, with his awakening scaling up again. Akainu >> Shanks. Akainu is also nullifying Kaen Daiko from Kaidou...Akainu x Mihawk is debatable, but I still put Mihawk above).

12- Kuzan (Akainu Full Power => Aokiji Awakening > Aokiji Ice Glove = Old Garp > Old Rayleigh with Haoshoku Haki coating => Kizaru <= Luffy Gear 5 (White Star Gun)... Ice Glove should be minimally comparable to White Star Gun. Kuzan's awakening must go head to head with Kaidou Kaen Daiko. I'm putting Kuzan above Kaidou because I don't think Kaidou's flames can overpower Aokiji's cold which can resist Akainu's magma which would literally burn Kaidou's flames)

13- Kaidou (Daiitoku Raimei Hakke => Kamusari. Kaidou Hybrid's strongest blow broke through Luffy Gear 5's defense and almost knocked him out. Kid would definitely pass out, maybe die from that blow. Kaidou still has Kaen Daiko who once again climbs him above Shanks)

14- Silvers Rayleigh (Prime) - (Rayleigh has Haoshoku Haki coating, but did not use it against Kizaru. Rayleigh Prime has a resistance of 3 days where it can maintain its coating. He is already moving up to Luffy Gear 5, so in his prime he is above Shanks' Kamusari. he could probably kill Kid with one swing of his sword).

15- Shanks (shot the child. From now on, few people would achieve this feat, one of them is Luffy with his White Star Gun)

16 - the Goroseis (Hypothesis)

17- Dragon (just a hypothesis. Dragon > Luffy)

18- Luffy (You may already be wondering why I'm mentioning Luffy so much in Powerscaling, but he doesn't appear. Leaving the explanation here, Luffy with Bajrang Gun in terms of AP scale => than Kaidou. But Luffy doesn't have good stamina, which would make it impossible for him to beat these characters above him without a good script)

19- Marchall D. Teach (While I don't see Blackbeard above Luffy, despite the narrative, Teach still has a lot to evolve. But let's talk about his talents. He also has a stamina of at least 3 days like Shanks and Rayleigh. He has an attack potency apparently superior to that of Big Mom as he completely incapacitated Law. Big Mom already knocked Law out once, but it wasn't definitive, so I think that Teach has more attack power, he's faster and more intelligent than Big Mom. in addition to having strong Hax that nullify AnM's powers)

20- Borsalino Kizaru (he has one of the best busoshoku hakis, he has excellent defense and speed, he managed to block countless attacks from Luffy Gear 5, due to his speed and defense I can't see Big Mom being the real problem for Kizaru who would gradually cause piercing/cutting damage)

Honorable mention to Garling, I still don't know where to put him.