wont face doesnt mean not strong enough.
Lanji can't do shit against kaido
- doesn't have fire cutting like kinemon
- doesn't have BS magic scroll like Yonko Raizo
- doesn't have internal destruction haki
- doesn't have 3 meito's swords with advanced armament
- doesn't have gamma knife
- doesn't have sound based cutting attacks
He would get shit stomped without being able to do anything , that's why Sanji is not facing Kaido