I think it would have made more sense for the Gorosei to be weaker and the Knights to be strong. The Gorosei could be primarily political, the Knights are fighters. Unless they did a backstory like the Knights are chosen to be political figureheads, while the Gorosei are the true string-pullers, who've had more time as immortals to get stronger.
Maybe Oda just found there's too many end-game antagonists for the Strawhats and their allies to fight: The Yonkou, Gorosei, Akainu/Admirals, Blackbeard Pirates, God's Knights. If the SHs have to keep getting stronger to beat each group, it would go on forever. Or if the SHs are basically at end-game power and those characters are all around the same level too, it's too many PK-level characters and too many equal fights in one place, so there can't be much focus on the main enemies (eg Akainu, Blackbeard, Gorosei, Imu).