To start I just want to say I do think Kaido is stronger than BM for pretty much the same reasons you do. My reply to you is more a self reflection on how at least the way I came to that conclusion is more subjective than I originally cared to admit.
I don't think the portrayals themselves are subjective but the interpretation of the portrayal to determine power level relative to someone in the same tier is subjective. For example you referenced the 1v1 bet on Kaido, Kaido strongest creature etc but it's not clear how these titles translate to a power level. Heck we had so many debates on what Strongest Creature means and how it compares to Strongest Man in this thread. BM has several things said about her that are meant to hype her and someone can make the claim that she has the edge over Kaido due to those portrayals. We can disagree with that person but the actual substance of our arguments wouldn't have any more weight.
As for feats, unfortunately they aren't very consistent in OP and they don't provide enough info to make the call when two people are close. I think we can both agree feats make it easy to put people into their tiers. But like you said its pretty subjective once you get to people in the same tiers since it's very difficult to use feats to determine who is stronger.
Is it really all that subjective though?
What is subjective of "1v1 always bet on Kaido" ?
I understand the conflict with whole "strongest creature" argument. Because there are people, including myself, who has thought that "creature" = "all species except humans". Which means, the title refers to basically other species - fishmen, oni, giant etc.
Same for "strongest man". Man here IMO refers to "humans" as a whole. Not all males in all species.
Now here is where the part without conflict comes in. "Strongest pirate" is a title without any room for interpretation at all. It simply means the strongest amongst those who are pirates. There are only two people who have held that title - WB and Kaido.
Kaido has also been referred to as the "strongest pirate". This was a title previously held by WB, which then got held by Kaido post TS.
Is there anything subjective about "strongest pirate"? Where is the confusion?
Lastly, lets even assume that Kaido and BM are relative in pure stats, even though the actual feats suggest otherwise (because we both agree that there is some wiggle room when it comes to feats).
But, having future sight when stats are relative, is simply better than not having them. Even if they are equal in every other stat, future sight makes the difference. Future sight isn't simply something we can throw into the bucket of wiggle room.
My next argument would be. Is there
ANTYHING Big Mom has over Kaido? Anything??
Yeah I think I'm pretty much on the same page with you on this one. Will be interesting to see an Admiral go all out before we get to anyone of stronger level on the WG side.
Yeah, I would agree with that.
I doubt Oda has the time to have them all go all out. But, especially one of the OG three at least should go all out.
I sited this example because it's one that comes up a lot but I don't think the core issue has to do with any particular characters. Honestly this is an inherent problem of creating power levels/taxonomic structures with the characters. Situations in the story are more complicated than our categorizations/buckets so we end up getting weird contradictions that seem wrong. In reality conflicting yet seemingly coherent thoughts are perfectly okay e.g. "I feel happy and I feel sad." I know some people would say wait that doesn't make sense, those are contradictions etc but I think contradictions are a part of it all. That is to say, I WB not on meds can be stronger than Akainu but still be weaker than Big Mom who we think is weaker than Akainu lol

Ehh, I suppose we just have to disagree on that lol.
If Akainu comes out to be an absolute boss in the next arc, that elevates old WB (out of meds) as well IMO. It would simply mean that old WB (in meds) and peak WB especially, were absolute monsters.
These are some good points. I think the first one makes more sense for our context since we were more discussing 1v1s, and not taking crews into consideration. These are all good ways to help us think through the contradictions for sure but also introduce their own potential problems to the power level dynamics.
I mentioned and compared the crews, because "crews" are a part of what makes a pirate a "Yonko". There can be incredibly strong pirates like Mihawk and potentially Aokiji, that will never become Yonko because they won't have crews.
Crews are also part of the discussion when it comes to comparing Yonkos.
There is an enormous gulf between WB's crew and the crew of Kaido/BM. Even more than the gap between even peak WB and Kaido/BM.
My point was simply to disprove the commonly held notion that Yonkos are in some kind of balance. Kinda.....but not really. Because two of the four OG Yonkos (namely WB and Shanks) simply had no plans for expansion or world domination.
It is a perception vs reality scenario. Especially as far as the casual OP world is concerned.
Perception: People thought WB was "closest to PK, closest to OP". Reality: he could've become all that whenever he wished to, but simply had no intention of doing so.
Perception: there is a balance between the four Yonkos that maintain peace. Reality: two out of the four Yonkos are chill dudes who won't bite unless unreasonably provoked.
There is nothing wrong with point 1, old WB (on meds) being stronger than BM. However, what this misses is that it was old WB (not on meds) that defeated Akainu in high diff way. However, old WB (not on meds) couldn't use CoC, had heart attacks, couldn't use CoO to not get stabbed by Squardo etc. These would make one think that BM is stronger than old WB (not on meds) since she can use CoC, can't actually get stabbed by someone like Squardo due to her durability, doesn't struggle with heart attacks etc. What does that leave us to conclude about BM vs Marineford Akainu? I'd say she should be able to defeat him in 1v1 at least high diff. However, that would mean that Marineford Akainu (who we all think is above average admiral) is weaker than BM (who we think is average to below average Yonko).
I completely get what you are saying.
As of now, I have no counter to this. If you ask me right now who is stronger, old WB (out of meds) or BM? I will say BM for sure.
I will say however that, even without conqueror's haki, Yonkos are still absolute monsters. WB still had the strongest paramecia fruit, which he mastered and was probably awakened (because WB can transfer the tremors to his blade and such, instead of just using it from his body)
Would BM get stabbed by Squardo? Absolutely not, it wouldn't even scratch her.
But, does BM have as much attack power as even old WB (out of meds) ? I highly doubt it.
Ultimately. My point would be that where old WB (out of meds) stand, is dependent on how strong Akainu turns out to be. Because there is one thing which absolutely is NOT subjective: old WB (out of meds) >= Akainu.
Wherever Akainu lands, old WB (out of meds) land right on top of it. Wouldn't this be the most obvious and logical interpretation? Unless of course Akainu is explicitly stated to have got stronger in the last two years (my default position is that Akainu is same level pre TS and post TS, because he is in his 50s and has peaked based on every pattern we have seen in the series so far)