He almost defeated Muzan in four minutes, a feat never before achieved from any other slayer in any era. It is obvious he is the strongest character in kny. He also scared Muzan so bad he had severe PTSD for centuries.
dkt is basically just a stronger Muzan that is immune to the sun therefore I think the fight would be somewhat close between yoriichi.
Strongest of all demons held off 6 hashira and the main character for a whole night and almost won. Way stronger than #4.
Way stronger than Upper 2, and would have beat 3 hashira but lost because he saw himself and what he had become and decided to let himself die. Can also regenerate his head which is an extremely rare feat among demons.
Douma has a better blood demon art than Upper 2 and below. He lost to a trick with an immense amount of poison while fighting two slayers who were both close to hashira level.
He literally clapped in a room full of hashira and stunned them all, way stronger than any slayer in the era the show takes place.
Upper three, he lost because he missed his wife and was able to regenerate his head. He solos the people under him (9,8,10). Also he killed 67 people when he was still a human.
Sanemi fought Upper Moon 1 and Muzan one of the strongest hashira. Relatively equal to Giyu.
Giyu fought Upper 3 and Muzan. He's also just super cool. Somewhat equal to Sanemi.
Single handidly beat upper moon 5. Also took on Obanai and Sanemi during a sparring match. Also his breathing style is really cool.