Last 6 chapters didn't spell out the clash over 4th RPG.
Buggy - has no RPG so he has to get hands over all of them.
Shanks before fighting kidd asked Hongo not about 4th RPG but about intel on Blackbeard - clearly indicating his focus is on BB.
Luffy and BB - both have to go for 4th RPG.
Yes, it's battle royale where their paths will lead them to 4th RPG - but it doesn't mean oda is hinting at 4 way match but that it's elimination one by one until one victor emerge just like how kidd and law got eliminated
The issue is unlike Law and Kid, Oda can and will not draw dedicated fights 10 v 10 between 2 Yonko crews outside of Luffy's perspective. Realize that with each clash, its practically one powerhouse vs the other (ie Garp and Kuzan). This, narrarively, does not work for Shanks nor Blackbeard when people keep ignoring key scenes about what he says or intends to do.
- Shanks wants to meet Luffy
- Shanks intends to go after One Piece
- Luffy wants to fight Shanks
- Shanks intends to go after Barto
One comment about Blackbeard does not signify any reason it takes precedent over anything else in the plot. They all are important, and nothing generally can happen without Luffy because theres no way Oda can simultaneously offscreen a fight between Teach and Shanks nor expose how each party fights. Its THAT particular thing that does not work for them, but works for Law and Kid because
A) we know how they fight
B) they were clearly small time compared to the 2 they fought.