I get what you're saying.It wasn't.
It doesn't mean there still weren't always 2-3 Pirates in the New World who were the most powerful and influential.
If Luffy can be considered an Emperor simply for:
Then the idea Emperors didn't exist is bad logic. Being strong and having a fleet aren't new things,
- Being strong.
- Having a fleet.
Shiki was said to have one of the biggest crews and we know of Rocks who had the most powerful and influential crew in the world 40 years ago, so we know Emperor figures did exist.
But there is a difference between characters existing who could qualify as an emperor, vs a system or world order actually existing as such.
I'm sure there would've existed pirates in OP, who were very powerful, had advanced haki, fleet etc
But, the situations, whatever it may be, that existed in the past, probably didn't allow them to outright become emperors that ruled over large swaths of land.
Let's even take the example of modern rich people vs rich people of the past.
Yes, the rich have always existed.
But, globalism and current world order has allowed the richest man, the power and influence over the world unlike what had been observed in the past.
There are no longer kings or emperors now in most of the world, but "democracy".
The system of governance can change, and has changed.
This could be the case in OP world as well.
There could've always been great pirates and strong men in general. But, only the system of the Yonkos........probably is a recent phenomenon.
There are two key events which might have resulted in the current order:
- Rocks, his ambitions and his fall
- Roger's death, kickstarting the great age of pirates