I don't really estimate how strong Yamato is like that? We have a floor for Yamato due to her impressive performance in Base, but we don't have a known ceiling.
I think Yamato's floor is "above all Tobi Roppo" (based on how Base Yamato treated Ulti).
So my belief is that Yamato is either above all Calamities or below them/on par with Jack. There really isn't any reason for her to be somewhere in between.
If Yamato's main fight in this arc is Jack, she's probably comparable to him/slightly weaker (she may evolve mid fight to win).
If Yamato's main fight is Kaido then she has no business being weaker than King. King level characters get low diffed by Kaido. I don't think Yamato will be getting low diffed by Kaido if he's her main fight:
- It's shitty storytelling. One Piece is a feel good Shounen. Even if Yamato is destined to lose, Oda isn't just going to write her getting destroyed the same way Post WCI Luffy was. Not giving the strength of the narrative behind their battle.
- Oda seems to be going for an epic fight.
- It's been 30+ chapters since Yamato was introduced and we've never seen her DF. Oda hinted that it's something incredibly powerful but refused to actually show it. He seems to be saving it for an epic reveal vs Kaido.
- Oda has interrupted Yamato's other fights against Kaido's executives, so there's a very good chance that Kaido would be the only major fight she gets this arc.
- Oda gave Yamato Kaido's exact fighting style and she can perform his moves identically. There's opportunity for very good fight choreography here.
- I'm expecting a "Father vs Son" confrontation. I think for storytelling purposes, the fight will be long (in terms of chapters).
So back to not knowing Yamato's ceiling. I think that because Yamato has no established ceiling, she would be as strong as Oda needs her to be in order to write the Yamato vs Kaido fight he wants to write.
I'm currently expecting Yamato vs Kaido to be a medium to high difficulty fight, so I expect Yamato to end up at the lower end of the Top Tier spectrum.
I expect King to be anywhere from Katakuri to Marco level. He might be stronger than Marco, but there's no real reason to assume he's a Top Tier.
So I expect Yamato to be able to beat King at High difficulty (if he's > Marco) and at medium difficulty (if he's <= Marco).
I don't argue for the above position in the arena because it's based entirely on my headcanon for how Yamato vs Kaido goes.
By current feats I have Base Yamato at Jack level+.
All of the above is based on two things:
- Yamato fights Kaido.
- Yamato doesn't reveal her Devil Fruit before she fights Kaido.
If Yamato vs Kaido does not begin within the next 5 Wano chapters (excluding arc breaks), I'll be pretty concerned.
If it doesn't begin within the next 10, I'll reconsider as Yamato vs Kaido clearly isn't playing out according to my expectations.
If Yamato vs Kaido starts soon, and Yamato reveals a Mythical Zoan with some connection to Kaido's (e.g. "Byakko", but a form of "Western Dragon" would also work as well), it would reinforce my expectations.