For me, the World is like a Ship, it has it's own Crew just like Straw Hats
However, instead of looking at Best Cook or Best Helmsman or Best Musician ... etc
Instead look for those who represent Closest to SHs Dreams
Mihawk represents World Zoro, because his Swordsmanship is Closest Example to what Zoro gonna achieve at the End
Big Mom represents World Sanji, because her Totto Land is Closest Example to Sanji's All Blue
Vegapunk represents World Franky...
Shirahoshi represents World Jinbe...
Leader of Elbaf represents World Usopp...
For example, you will soon discover there is already Someone who Drew a World Map, but it's Inferior Version to what Nami gonna make EOS
... etc
Based on this, i believe Strongest & Greatest Pirate in OP Currently and possibly all time is the Man who represents World Luffy, meaning since Chapter 1, He already achieved an Inferior Version of Luffy's Dream (Not PK, his Real Secret Dream), and i believe that's Sea God, someone who most Pirates would follow if He ever decided to say "Hi"
And i'm not gonna bother mention all Speculations & Theories, but just check God's Valley Incident & you'd realize that there is something that all Pirates value regardless of which Crew or Faction They follow, it's like their Religion, a Pirate God, someone like Davy Jones
So imo Strongest Pirate is not Introduced yet, but He was pulling the Strings from very beginning, and if you want an example of Pirates who follow such Man, don't look further than Blackbeard Pirates, They literally won't shut up about "Fate", you think They are Muslims or Jewish or Christians? Ofc not, They are referring to their Pirate God
Don't be surprised if Blackbeard is Jango of the Story who is preparing everything for his Kuro, the Hidden Actual Strongest Pirate.