So he didn't use haki against the scabbards but did against Luffy? It makes no sense.
He didn't use haki back then and didn't in this chapter.
Katakuri had superior haki over Luffy yet when Luffy used G4 he was still bleeding. With enough strength you can bypass CoA, but Kaido's scale are special.
Does he need to be in Zoan form to use his powers? No he's currently lifting Onigashima while in base.
Luffy G4 >> Scabbards, why does not make sense for you?
No, Kaido' scales are not special. You only need enough AP.
Advanced Haki lvl 1 is = +AP, nothing special.
The one which is special is Advanced Haki lvl 2, which ignores the external defence.
It wasn't said anywhere that he has scales in Base. That's pure assumption.
Bro Doffy is cleary visible and super black, The hit on Kaido was just shaded. That's it.
Even in the anime there was nothing.
You're grasping at straws trying to minimize Luffy's growth.
Kaido's one is clearly visible as well. You can check it with other hits against a body (other examples in the manga) and see if in any other case that shading exist.