The Shichibukai are not a big faction outside this manga lol? The knights of god would be iconic as Hell
Yeah maybe they'd be iconic
if they played a role earlier
But all of the manga with super iconic groups of antagonist typically have them play a role in the middle of the story
at the latest. You're comparing antagonists that were either setup from the
very beginning of the story (like the Phantom Troupe and Akatsuki) and antagonists that were relevant when the main cast was significantly weaker (like the Espada) to secondary antags in the Final Saga
If you wanna argue that they should've been introduced earlier then that's one thing. Go ahead
But to say that other authors could accomplish more with the same structure is baseless