If Zoro and Sanji put aside their differences they become a really formidable duo. Plus both can use Armament Haki which bypasses Logia devil fruit defenses. Kizaru’s only way to avoid getting destroyed is he keeps his distance but Zoro and Sanji are good at closing the gap. If they didn’t hold back and didn’t waste time bickering they’d likely crush Kizaru with enough effort
Luffy was equal. When he beat Kizaru he ran out of energy, causing a tie. After they were unable to move, Kizaru recovered first and then fed Luffy, showing us he wasn't really trying.