There is a difference between invisible CoA and Hardening though, hence people mocking Sanji.
Nobody is denying Sanji having CoA, confirmed several times, but he still has not shown in a fool proof way that he has Hardening.
For invisible CoA, yep most of the times people comment on it (Sentoumaru, Luffy vs Caesar for the first time, Sai´s brother in the colosseum, Tashigi vs Monet), but Hardening is a different thing.
And Oda won´t go Sanji has Hardening, so unless it is shown, it´s not confirmed. I thought maybe black lightning is indication, but Sanji himself used invisible CoA with that.
Law´s main attacks, his slashes, are useless vs Logia, and Smoker pressured Law in his main weakness, CQC. Same thing Hawkins did, same thing most mid tiers can do if they are skilled in CQC, and that´s Smoker´s main strength.
And even then he lost low to mid diff.