You can't make a ranking of people who were killed due to the plot, and not take into account their prime potential. If Oden was still alive today he would be at the very least >= current kaido.
And he wasn't One shot,since he felt like nothing in the next panel, it's just his nature to go fight every oponent like that, and when you go like that you have to confront their attacks and understand it after. Exactly like what luffy does : He always attack without thinking, and get hurts even by fodder or non top tier for a few minutes - last case was vs Apoo and Zorro had to save him.
And that was not the Oden who fought vs Kaido, Oden was weaker there, let alone prime Oden - he never reached his prime due to plot and Oda;
So does that mean that Zoro defeated the 4th strongest underling of doflamingo and needed help to do it?
The crew went Vergo > Rosinate > Trebol > Pica > Diamante
Anyway Oden is dead homie, his corpse isn't doing anything, you're lucky I'm including him at all. Also since your post is essentially just saying kaidou isn't shit, the point is that kaidou got stronger. Also you could argue that SHiki, Captain John, Silver Axe, etc could have gotten stronger if they weren't
1) Removed of their legs + had a steering wheel of a ship in his head
2) Dead
Also prime big mom is arguably stronger than current big mom tbh, she was the type who was born strong and the old age and brain damage probably slows her down, so I'd still say the power scale stays the same.
Oden can hang with Roger/Whitebeard when they aren't going all out, but once they go all out with their advanced probably haoshoku is what it was, he's a child. Shiki and the others can hang with serious Roger and Whitebeard, albeit still lose, but rival their power.
That was the strongest Oden was.
Honestly Oden was a retired pirate who was going to coast in wano and was on the pirate kings ship. Kaidou kept being a pirate, so realistically, Oden was probably only going to be nerfed like rayleigh was due to inactivity, not bolstered like kaidou who kept big dicking his way through life.