Zoro represents power.
Sanji represents emotions/passions.
Zoro's counterparts only have to show power to fit his theme. The fights in themselves are enough.
Sanji's counterparts, on the other hands, have to show those passions, which leads to gags or backstories explaining why they express their passions in a certain way.
Just like how Luffy represents freedom, so his opponents have entire plots detailing how they deprived others of freedom and why.