Then why BB is the only character who specifically said "the world" and not just one piece?
The world here encompassing not just one piece but the highest authority - the throne
Must all Characters use the Same Words?
One Piece is just Name that People around the World chose for this Treasure
Roger himself didn't call it "One Piece" when He was Executed
He simply said "My Treasure"
As i said, Roger's Treasure is just what Everyone considers to be "Most Valuable Prize"
They don't care what it is, They simply believe They can Buy whatever They want with it
In Last Chapter, Auger said "The World" meaning that BB Pirates Goal is to "Buy The World"
Which is why i mentioned Sandman's Tweet, as it's Confirmed that Oda was gonna make Roger say the Exact same
But what does BB Pirates mean with "The World"? We don't know that
What We know is that owning One Piece makes you Pirate King & allows you to Buy Anything
And what did Narrator say Pirate King has? Wealth, Fame & Power
Meaning "The World" = Peak Fame + Peak Wealth + Peak Power
And Price for Buying this is finding One Piece Treasure
It's a Story about Pirates, & what do Pirates do? They Plunder & Pillage & take Loot & Steal ... etc
So Pirate King Title automatically goes to anyone who Successfully Plunders The World (It's Price is called One Piece by People)
So Highest Authority isn't Superior than One Piece, it's Part of what One Piece can Buy you, it's only Third of what The World has to offer
One Piece = The World = Being Highest Authority + Most Powerful + Wealthiest
Just like Enel, He took Goro Goro No Mi to become Strongest, Invaded Skypiea to Rule All Sky People & took Shandia's Gold to become Richest, when He combined these Three, what did He Build? (Using his DF, Gold & Authority)
He built Maxim which took him to The Moon (His Real Dream)
Blackbeard is just like Enel
Just replace Goro Goro No Mi with Darkness DF
Replace Skypiea with Mary Geoise
Replace Shandia Treasure with Mary Geoise National Treasure
Replace Maxim with One Piece
So when Blackbeard says "The World", it means that his Plan is:
1. Acquire Strongest DFs (Already Did)
2. Invade Mary Geoise (In Progress)
3. Take their National Treasure (Soon)
4. Claim One Piece using Power, Wealth & Authority He just Acquired
5. Use One Piece to reach his True Dream (Which is still Unknown)
I'm not saying Last Chapter doesn't tease BB possibly being Final Villain, but i'm saying that it didn't reveal BB's True Goal, it simply Teased He has One & how He intends to reach it