PERSONALLY I believe it's a mistake to make a distinction between ''barrier'' and internal destruction and that's what Luffy was using before adding CoC, some might bring up the tree training but at no point was Kaido going to explode the same way other antagonist haven't exploded previously despite Luffy's punches being able to vaporize rocks before too, now there might be people that still think he wasn't using it because he was making contact but Luffy has beyond doubt shown that making contact and using internal destruction aren't exclusive since that's how he destroyed collars and handcuffs.