Placing One Piece characters in lists is really difficult, but i'll try.
This is my list while not including old legends(Whitebeard, Roger, Rayleigh, Shiki, Garp, Kong, Sengoku, and so on)
1- Kaido
2- Blackbeard
3- Mihawk/Shanks/Dragon/Akainu
4- Mihawk/Shanks/Dragon/Akainu
5- Mihawk/Shanks/Dragon/Akainu
6- Mihawk/Shanks/Dragon/Akainu
7- Kuzan
8- Big Mom/Borsalino
9- Big Mom/Borsalino
10- Fujitora/Greenbull
11- Fujitora/Greenbull
12- Marco/Ben Beckman
13- Marco/Ben Beckman
14- Jack/Jozu
15- Jack/Jozu
16- Doflamingo/Inu/Neko/Sabo
17- Doflamingo/Inu/Neko/Sabo
17- Doflamingo/Inu/Neko/Sabo
18- Doflamingo/Inu/Neko/Sabo
19- Vista/Luffy/Magellan
20- Vista/Luffy/Magellan
21- Vista/Luffy/Magellan
22- Ace/Kid
23- Ace/Kid
24- Law/Drake
25- Law/Drake
26- Hawkins/Zoro
27- Hawkins/Zoro
28- Apoo/Kuma/Ivankov/Hancock/Burgess
29- Apoo/Kuma/Ivankov/Hancock/Burgess
30- Apoo/Kuma/Ivankov/Hancock/Burgess
31- Apoo/Kuma/Ivankov/Hancock/Burgess
32- Apoo/Kuma/Ivankov/Hancock/Burgess
33- Killer/Urouge
34- Killer/Urouge
35- Capone/Bonney/Vergo
36- Capone/Bonney/Vergo
37- Capone/Bonney/Vergo
38- Sanji/Smoker
39- Sanji/Smoker
40- Pica
This list also doesn't count non-introduced(or featless) characters like Kaido or Big Mom's FM, Wano Shogun and so on who could possibly be high in rankings. Though i'm quite uncertain with placements of characters like Hancock, Kuma, and related ones(Ivankov, Magellan) because i find their standing unclear in the manga. Didn't place characters like Shiryu either because he is most likely even stronger than preskip. Characters like Sanji or Smoker also suffers in my list due to their Punk Hazard feats as well as portrayal not giving that much emphasis concerning potential strength, but could change with time. I placed the guys in the worst generation not based on feats(almost none of them have) but based on how i felt their pre and post-skip portrayal implied them to be, another subject of a change then when we'd get a clearer picture
Also the gaps are smaller than they appear to be in ranking. There are many in my lists capable to give the ones above extreme difficulty fights, but are rated below due to lower portrayal and potential
Furthermore if i were to place the old legends(in their prime), Roger and Whitebeard would share the number1 spot infront of the Garp/Shiki pair who themselves would be infront of the Kaido/Rayleigh pair. I'd probably place Sengoku at Big Mom/Borsalino level. Chinjao was likely at Vista/Luffy/Magellan range. And i don't know where to place Kong(not enough info) outside of the fact he was in the admiral range