What's so complicated about those Titles?
They are Epithets given by People themselves
In OPVerse They were like, who got Strongest Power? Whitebeard, so let's call him Strongest Man.
Who represents Highest/Strongest Life Form? Kaidou, so let's call him Strongest Creature.
Who is Best with a Sword? Mihawk, so let's call him Greatest Swordsman.
Who succeeded the most as a Pirate? Roger, so let's call him Pirate King.
His Right-Hand Man should take comparable Credit, let's call him Dark King.
Shanks, WB, Kaidou & BM are ruling in New World like Kings? Let's call them Yonko/Four Emperors
... etc
Titles are only meant to show you that these People are the best at that particular Job.
No one uses a Sword better than Mihawk, no one had Greater Power than WB during his Lifetime, no one represented Stronger Life Form than Kaidou (From what is Known), no one achieved in Piracy better than Roger, no Pirate is having more influence than Yonko ... etc
No need to think too much about who They include