I'm not jealous over a title, I'm just trying to point out that someone who is "said to be" something doesnt mean they ARE. Also, definitions can differ depending on context. Even in the seibutsu that you posted, they make a distinction between living thing and creature. Have you ever asked yourself why Worlds Strongest Man/Worlds Strongest Creature are separate titles? It's almost like... theres a distinction. And given the coexistence of WB having the WSM title, and Kaido having the WSC title, this seems to indicate that within one piece, creature does not mean literally every living organism.
I will seperate this into 2 categories after that i will not gonna write anything about this subject.
1-Said to be means that its accepted by the people that Kaido is the strongest. And it is heavily implied that Kaido is really the strongest.
Also So many characters in this series called him the strongest too. Zoro, Killer etc.
After all of this thinking that Kaido isnt top 1 right now is ignoring all the implications and the title from Oda.
2-Kaido can be the strongest while WB is old and weak. Since Kaido isnt human as you said.
But Kaido's title literally means that he is the strongest living thing right now.
So i will believe in Oda's words and his implications then anything else.