Warlords are okay, Crocodile and Doflamingo actually played well.
Same for Kuma.
Admirals are unique, the best group, best well writen characters who carries One Piece.
Yonkou are not bad either, at least im sure Shanks and Teach getting great stories.
Also yes Big mom threatment was poor, but hell her performance pre wedding cake was great and her flashback was insane good.
Kaido had power but lacks in character, pretty boring if you ask me.
For fight, he is great, but Oda failed to give him a proper character flaw/background build up.
Admirals have both, power and great background story.
Alone the fact that Oda plans to make them the final villians before Imu, tells you a lot about them