Kaido and Big Mom were not well written villains. Hell they genuinely didn’t even feel like they were planned based on how disappointing both were.
The best written yonko are buggy and Blackbeard. Those two have still been some of odas best work and I’m sure shanks still also be up there once oda gives him more focus. Just knowing shanks is living a life he didn’t want is interesting so hopefully Oda expands more on that.
What you smoking? BM is the most well-written Yonko Oda has given us so far:
-Interesting backstory that's tragic and ties deeply to the events of a future arc
-Clear goals with multiple facets towards that goal including becoming PK, using science to gigantify, create a paradise with all races
-History with multiple Yonkos including brother-sister relationship with Kaido
-Powers that are far more creative and interesting than just 'muh black lightning'
-Knows much more than she leads on, including hints to OP, Lunarian race, God Valley events, etc
-Arrogant personality that becomes her own downfall yet endears her as an avenger that won't accept defeat even till the very end
-Contrast age visual appearance that shows her decline but leaves imagination open as to how she was when she was still beautiful
Oda put a lot of thought into BM despite being a secondary villain in Wano. The fact she keeps getting mentioned and her powers referenced also shows Oda actually likes the fat bitch on the side