See that was my original thought as well, the six powers being the early base before Oda had completed the idea of haki. That can still be true but i still think iron body is different than armament haki now because of the description of iron body being capped by physical strength while haki can be strengthened
1. I still do catergorize tekkai as being different from armament hence why I made the comment of coby combining both for strong defense.
2. Geppo/sky walk and tempest kick are definitely ryou based though. So is rokougun.
The whole kicking air doesn't make sense since we have heavy people use it (so it isn't size based) and we have people with weaker leg strength use it while some stronger legs fighters can't (so it isn't strength based)..
Instead it has to be the projection of ryou that allows the user to platform on the air since speed isn't even needed to sky walk since we saw Lucci do it while being completely still in the air.
It's the same for tempest kick. A slicing attack from a kick doesn't make sense unless the projectile from the kick was sharpened. We learn that swordsman with ryou do this.