Oda chose 4 Emperors only before because he always planned to finish the series with these 3 replacing other 3 in the Final Saga:
- Teach (Logia+Paramecia, and will be strongest man) was going to replace Newgate (Paramecia, and strongest man).
- Luffy (Zoan, Joy Boy) was going to replace Kaido (Zoan, and wanted to be Joy Boy).
- Buggy (Paramecia) was going to replace Linlin (Paramecia), Linlin never fought Luffy in a big 1 v 1 battle, instead Linlin's 2 commanders Katakuri and Cracker did. Same way Buggy won't fight Luffy, Buggy's 2 commanders Mihawk and Crocodile will fight, either they will fight Luffy or Luffy's commanders Zolo, Sanji and Jinbe.
- Teach (Logia+Paramecia, and will be strongest man) was going to replace Newgate (Paramecia, and strongest man).
- Luffy (Zoan, Joy Boy) was going to replace Kaido (Zoan, and wanted to be Joy Boy).
- Buggy (Paramecia) was going to replace Linlin (Paramecia), Linlin never fought Luffy in a big 1 v 1 battle, instead Linlin's 2 commanders Katakuri and Cracker did. Same way Buggy won't fight Luffy, Buggy's 2 commanders Mihawk and Crocodile will fight, either they will fight Luffy or Luffy's commanders Zolo, Sanji and Jinbe.