Big Mom has been far more disappointing.
She went from being this supposedly smart, capable, competent, powerful individual to a dumb, incapable, incompetent, glorified punching bag.
Even now in Wano, she got neg diffed by King and fell into the ocean despite the fact her dumbarse can literally fly and then lost her memories in a Scooby Doo level plot twist. Her humiliation is only further cemented by being used as a overweight meat shield by the Straw Hats and getting her skull cracked by Queen.
This is without even getting into the details of her inglorious portrayal during Woe Bake Island.
As for Sanji, the only things I did not like was how the whole Vinsmoke plot was not actually resolved and how his cooking skills went nowhere.
It was not even Sanji’s idea, it was Pudding’s and apparently Chiffon was just as necessary as Sanji.
The entire Cake Plot was dumb. It had Bege acting completely out of character compared to previously, Pudding acting ridiculous, Big Mom getting consistently humiliated and Sanji helping to create a cake that no matter how you look at it, failed, proving the detestable Vinsmokes right all along.
The cake fully healed BM which is incredibly strange considering BM was physically healthy when Sanji left to make that cake and it did not even stall BM long enough by it’s own merit since Chiffon had to make a longer trip and all the Straw Hat’s allies had to stall a full power, healthy Big Mom.
The cake failed, end of.