The Shichibukai is an incredibly one sided deal in favor of pirates. Hence that system was abolished. You get immunity, can build your empire if you wish and enslave countries and don't even attend meetings. Mihawk was the rarest guest and when he came, it's for his own interest. Even in an event as important as the MF war, the Shichibukai had their own agendas and were there for the fun.
Sounds like a great deal. Doffy was literally the biggest underworld broker, supplied countries that fight each other with weapons, supplied Kaido with smiles, controlled a kingdom and enslaved its people and the Marines didn't touch him.
Sure. On the one side we have corrupt pirates that turn the world into a paradise for pirates while having immunity and being unreliable, on the other side Lunarians boosted by the abilities of the Shichibukai and DFs, being completely obedient and probably still being improved.