That would just make Blackbeard a second-rate upstart that shows up after the main villain has already been dealt with. I don’t see how that could be satisfying.
Blackbeard is a dark reflection of Luffy, but Imu is the direct opposite and the reason for Luffy’s fight for freedom in the first place.
It’s because of Imu’s subjugation of the world for 800 years that Roger created the Great Pirate Era to search for the One Piece.
It’s because of Imu that so many Strawhats and Luffy’s friends (and enemies) all over the world have been suffering:
- Marines almost executed Zoro because of corruption
- Arlong oppressed Nami’s village because of the WG’s oppression of Fishmen, and also the Marines working with him
- the Shichibukai were given free rein, hence Vivi, Brook, Rebecca, etc all suffered
- Robin’s homeland was destroyed and she was hunted since she was 8 years old
- Franky lost his father figure Tom and most of his body
- Jimbe lost Fisher Tiger and Hachi & the rest us to face racism against their kind.
- Ace was executed for being the son of the Pirate King.
The WG is the reason Iceberg & the rest of Galley-La in Water 7 were almost killed, that mermaid Camie was almost sold into slavery, that Luffy thought he lost his crew on Sabaody, that Ivankov & Bon Clay were imprisoned, that Sabo was nearly killed as a child, that Caesar could experiment on children under a Shichibukai, that Smoker & co nearly died for investigating it, that the Minks have been waiting for the dawn, that the Lunarian genocide occurred, that Big Mom grew into a monster because Mother Caramel wanted to sell her to the WG, that Kaido wanted to start a war with the Celestials, that Vegapunk was killed.
Blackbeard is and has always been a drop in the ocean compared to all that…and he’ll likely turn out to be a WG victim just like the rest of the Yonko.