Gamma Knife? of course, it is less powerful than adv CoC+internal destruction at internal destruction and Luffy can take some of his own attacks.
Ashura? Yes, it didn't put Kaido on his back, luffys base adv CoC punches did.
Do you think a single scar puts Luffy down? Wtf, he had his organ drilled into badly by Katakuri while drugged and carried on fighting for hours when he was only YC level, let alone now he is yonko level.
Even if you think humanoids like Luffy that regularly take haki infused blows with tremendous damage capability are fragile enough to fall to a few attacks, when their peers don't, and Luffy and Shanks will be tremendously fragile relative to Big Mom and Kaido (despite being able to withstand their yonko level attacks), that still doesn't mean Luffy hasn't surpassed Kaido, it means he hasn't surpassed his damage soak and zoan regen, Luffy's raw speed, attack power, haki, brute strength, tenacity, etc. can all be above Kaido and will be by the end of the arc.