Luffy was fully focused on Kaido in 1vs1 and extremely fatigued "barely standing" as per Yamato's own words.
He got blindsided by an external assasin involving himself in this extreme diff fight.
That is different to getting stabbed by someone far weaker than you in a 1 on 1 situation.
WB could detect Ace trying to kill him while sleeping when his haki was working properly in ch552...
Doflamingo can stitch organs, but characters who can phase their bodies into amorphous elements have no durability benefits... Oh wait we've seen haki users slash Akainu's neck and him be fine afterwards...
It's not headcanon, the WB that fought Shanks was not in the same heart attack prone, deathbed state. WB specifically laments the fact his haki isn't working in 569 saying he can't stop them, just before Luffy does it by accident, do you even read the manga bro?
You're full of crap here man
CoO needs to be activated.
Kaido doesn't sense the Scabbards are coming
Akainu doesn't sense Whitebeard sneaking behind him
Katakuri doesn't sense Luffy bursting out of mochi prison and ruining his tea time
WB did not activate CoO because he didn't need to
Marco never says WB's haki is the issue, he says his physical condition got worse, haki is not tied to physical ability, he was refering to WB's innate reflexed and ability to dodge in itself
Secondly Doffy isn't a logia, Akainu was never actually hit by Marco/Vista because he shiftshaped to avoid the blows, so how are you gonna compare these instances to WB cleanly hitting Akainu and making him BLEED?
Also cap WB was 100% confident he could use CoC, the hole Akainu had just given him prevented that from happening