I mean, it can look the same and still be of different power. A hakiless Shishi Sonson looks just like a hakified one. It's not just about AoE. Oden's Togen Totsuka didn't look spectacular, but it almost one shotted Kaido.
Also, what do you mean with CoC-less Oden? it's not like CoC increases Oden's durability. Also keep in mind, that Oden was portrayed as a natural freak. Who slammed the nurse against the wall at birth, who obliterated a bear at the age of 5, taking a bath in boiling oil for an hour, etc. So that freak of nature tanking a slash from Roger that wasn't really meant to do much harm vs. Shanks having the intend to destroy Kidd and doing so, I don't necessarily see the contradiction here.