
Only one left from Kaido's top 5.
Kid and Killer declares Kaido as strongest:

Then they face Shanks, who is declared as top 5 by Kaido.
After Kaido's death:

''Our commodore's the greatest''
BB's crew is obviously biased, but I don't remember BM or Shanks crew saying their captain is the ''greatest'' when Kaido and WB were alive.

Rayleigh confirms Teach is stronger than him, while Garp was putting Rayleigh in a same category as WSM Whitebeard;

WB - 5 billion, and Kaido - 4.6 billion, bounty difference is more than 350 million.
Kaido - 4.6 , BM - 4.3, difference is more than 200 million.
-
Shanks -4, BB -3.9, difference is less than 50 million.
They follow each other movements:

So it looks like the only thing that stops Shanks being WSM, is BB.
Vice-versa, the only thing that stops BB being WSM, is Shanks.