Sanji’s position on the ship, his job, is cook. Zoro is a combatant/fighter, which is so true, because he literally uses a deadly weapon, but three of them. Zoro will continue training and fighting foes. The hard work paid off so he earned Coc.
Sanji is always going to fight, but he relies on his fire ability with no weapon (cig is a weapon?). That was the theme of WCI. Sanji will always be slightly less powerful than Zoro. Sanji isn’t shown training so yeah he is a cook. His mother died so that could’ve weakened him.