Ahh so coby
Cool.
Luffy stated that kaidos scales made him tanky lol hence why he learned ryou to penetrate his scales: luffys words lol.
Negating devil fruit ability has nothing to do with one's durability so that is also a mute point
Address the other points as well.
What is more likely,
A) Coby, a cool specialist, who awakened his coo first, who was hyped in the use of coo, who had an emotional episode because of his coo, using that and dodging some aoe attack from Boa?
Or
B) Coby suddenly being this haki monster, having haki the level of Yonkers and top tiers, and negating a df attack by tanking it completely?
OCCAM'S RAZOR. look it up.