You know, people of AK had enough technology to create weapons of mass destruction and seeing how the big issue of the century, according to your theory, was the unificaion of the seas (or may I say, having issues in crossing the sea around the world) wouldn't be much easier to just try to create another way of locomotion? Like, a plane or something that doesn't have to do with the sea?
Speaking of which, why aren't there any means of air transportation in One Piece? Even Eneru pulled that ballon/air ship thing that I forgot the name - And Vegapunk could do something much better than that IMO (I don't know if this is kind of off-topic, but I always had this question with me but never got an reasonable answear)