That’s a very weak assumption predicated on mere speculatuon tho. Because it’s already been heavily implied that they’re intertwined or at the very least linked successively like Punk Hazard to Dressrosa for example.
The nature of WB’s statements in Marineford simply paints it as such:
Finding Raftel and the One Piece basically means kickstarting a great war vs the World Govt, i.e kickstarting the final war. That’s the takeaway.
I don’t see any reason for Elbaf being that long tbh. It looks like its going to be an intermission arc where Ussop gets some development and I think Oda will shift the tone drastically at the end via revealing the Red Hairs falling to Blackbeard and ultimately setting the scene for the Straw Hats facing the Blackbeard Pirates post Elbaf. That conflict spills over to Raftel, Blackbeard falls, Luffy is crowned Pirate King, Final War begins....you get the point.
There’s plenty of time to meet Vegapunk and have him do his DF expose’ Post Elbaf, in fact BB’s mystery could be unraveled via Vegapunk simultaneously as BB is in action vs Luffy.
The 4th road poneglyph could very well be hidden on Elbaf as well.