Well, Kaido was the first top tier who 1.) went all out, 2.) showed all 3 levels of Haki, 3.) demonstrated some island level attacks, 4.) was beaten by Luffy.
I'd say Kaido is a mid to high top tier but he has a clear disadvantage that he isn't awakened. Oda just needs to bring up awakened top tiers and Kaido can quickly look outclassed.
I don't even think Loki's gonna be the last character, aside of EOS Luffy, BB or Imu, who's powercliffing Kaido.
Another disadvantage is that he got beaten by Luffy who learned ACoC in like 3 hours and just unlocked G5.