Longinus was shattered before Sanji fully unlocked CoC... And how did you measure Sanji's ACoC to be above Yamato?
Yamatos acoc is so bad that it could not even compare to Kaidos weakest acoc attack WHILE NERFING HIS HAKI, the same attack that Zoro took while having 30 broken bones and still was not KO, same attack law took and easily fought after that Big Mom. Sanji Power is not only acoc its multiple things going together, its his insane flames+insane dura+his stronger coa+ at that time lower lvl acoc.
thats what broke the weapon, Yamato does not stack multiple buffs like that instead is just the lowest lvl coc user we basically ever saw. Luffy 1 second coc awakening was already stronger than Yamatos strongest attack. same with Sanjis coc