My first reply in the website
for me, yes he most likely is (excluding characters who hide in the shadows, the likes if Im-sama or others who Oda might reveal to be strongest in history not just one from one era)
As for the Big Mom tied with him, I would be disappointed if any of 4 yonko lost during 1 single night to get overwhelmed during their skirmish!
Regardless whether Kaido is strongest or not, 4 yonko are supposed to stand close to each others in strength to a point that allows them to have an equal fight for MANY DAYS
Otherwise, they are a joke, and fights like Ace - Jinbe that took 5 days, or admirals that took 10 days would make Yonko look rediculous!
So, look at it in the same manner as Akainu vs Aokiji!
Kaido and Big Mom imo the result of the fight would be Kaido winning imo BUT it would take a whole lot of difficulty to achieve it, and many days!
So, I think most people in their ranking now put Akainu above Aokiji in strength, BUT the fight was almost equal and lasted for 10 days, but in the end, Akainu got the better edge and won.
Any yonko getting overwhelmed fast would only put shame on the title of Yonko
As for Big Mom not having Zeus or Prometheus, let's all remember that she is a paramecia user, while Kaido is a Zoan, meaning he didn't go to hybrid form as well! So he held back as well
Regarding Oden injury to him, first we need to consider those factors:
1- How strong is Oden! It is obvious Oda love to wank Roger's crew! In fact, based on what Jinbe stated about "crew member of future pirate king shouldn't be intimidated by a Yonko" only adds to Oda's mentality and how he pictures the crew members of pirate king at their prime and they reached the peak of strength could actually face a Yonko head on. Specially the top tiers fighters of the crew.
2- How strong was Kaido 20 years ago, was he a yonko already? close to them? maybe less? no one knows. people downplay Kaido for an event 20 years ago, when Blackbeard was damaged by a pre-timeskip level Luffy Jet Pistol and screamed in pain!
So, you gotta factor both, Oden and Kaido's level
and if Oden anywhere close to Rayleigh in level (I think he's slightly below Rayleigh) then I am expecting the same result with all other Yonko where Oden would have damaged them as well