Just get one thing straight, People hit their prime in 39~40. And loose it by 55~60.
When whitebeard was 39, Kaidou was 26, Mihawk was 8.
- Whitebeard at 39 was WSM.
- 13~14 years later, Kaidou took the mantle at 39~44 , Whitebeard started to decline. Mihawk was 21~24 at that time, Just like Kaidou, already made a name for himself even before great pirate era.
- skip it more to 20 years. Mihawk is currently 44, Kaidou is out of the picture, So is whitebeard. He is world strongest right now.
These people prime never existed at the same time. After their prime they just carried the Title further, doesn't mean they are still the strongest.
This list basically involves Admiral, Warlords and Yonkou. Because these are the only top tiers people know about.
Imu, Gorosei are unknown, nobody knows about them. So they shouldn't count. All three are alresdy stronger than Gorosei. So Imu is the only exception as of now. When oda say strongest title is official, and people talk about it, look at it from one piece regular point of view. Not yours.
Hope that ckears your doubt Albino chan.