Kaido and Big Mom aren't the second coming of Rocks. Blackbeard is.
The Rocks storyline is setup for EoS, not now. Kaido and Big Mom were only peripheral figures to it in the past- an apprentice on the crew and the, at best, third strongest member.
The main story of Rocks is D related, Void Century related. Why three separate D's, Rocks, Roger and Garp, all came together and fought at an island named after God, with the Celestial Dragon's involved. Kaido and Big Mom's alliance is just a warning shot, before the real deal, Blackbeard, comes along. He's the actual Rocks successor. A D, the only man with two DF's, a host of deadly backstabbing pirates under his command, the enmity of Im alongside Luffy, a flagship named after Rocks, in Rocks' old island, and in general just a vastly more important character than BM and Kaido are. It's with him we get the payoff for the Rocks story- Kaido and BM are just the beginning of it.
the Marines see their alliance that way, and Oda seem to be pushing the idea, to the point where just BM calling Kaido made the Marines recall the Rocks Pirates and were afraid of them coming back
I don't see how it is EoS material, if BM and Kaido were there, and know everything there's to know about the incident why it can't be their story? or rather Kaido story?
I also don't think it matter how strong they were back then, what matter is how much God Valley incident affected them and how much its relate to their future goal(especially Kaido), if anything Kaido being young back then suggest the incident probably heavily infeluenced his character and goals
I get that Rocks story could be related to BB, but that doesn't mean Kaido and BM's aren't , they all could be in different ways
I see Rocks story as the history of all major pirates and are equally involved in it, otherwise there's no reason to shoehorn characters like WB in it
to the most important point, I completely disagree that BB is way more important than Kaido and BM, and I don't think Kaido and BM won't be involved in any major story element
because what you're basically suggesting is Kaido and BM are filler villain with no relevancy to the story, because the thing is unlike past villain who luffy defeated this it for Kaido he's gonna be Killed, while past villain will comeback and will still play a role and add something to the story, Kaido won't have the chance, so his major role and the reason he's part of the story need to be shown in this saga, I don't believe oda will make the mistake of portraying Kaido and BM as just strong irrelevant filler villains
the build up to Yonko/Kaido saga started from thriller park up until know, arcs like Thriller Park, Shaboady, partly FI, PH, DR..ect were all build up to this saga, all of it just to make Kaido story about defeating a strong pirate? while anything related to EoS will be about BB? I highly dought that's what Oda is planning
Oda said OP was a story about Luffy fighting Yonko, and given that most of the story was build up to their saga I don't think Oda will make two of them that irrelevant
Sengoku actually agreed with Sakazuki that they shouldn't go to Wano.
I recall Sengoku saying he understand Akainu decision? maybe am misremembering, but his last quote seems to suggest he think there's something weird about Wano and telling Akainu maybe he should interfere