Right, Oda is very intentional in everything he do, maybe there is a difference.
But still we can split this feat into two:
Where weapons touched:
Shanks vs WB
Big Mom vs Kaido
Where no physical contact:
Roger vs WB
Kaido vs Luffy
So, we have seen WB, Kaido, Roger, and Luffy using "no physical contact CoC".
On the other hand, there is Big Mom and Shanks. We have seen them split skies but with physical contact of weapons.
What would you conclude from this?
Big Mom and Shanks have lower or advanced level of CoC as compared to Roger, WB, Kaido, and Luffy?