Greenbull is clearly overreacting there, even if thats probably the most impressive CoC display in the manga. He has a very expressive personality (to not say slightly a clown)
He also got caught distracted and completely off guard, which makes a huge different on how you receive that offensively
The fact he put his hands up is another proof of overreacting, especially when Shanks was communicating to him from miles away out of nowhere
The fact Momonosuke and Yamato were celebrating the fact Greenbull was leaving them shows that he was simply walking away while talking during the whole thing with his hands up like "Ok ok, im leaving anyway", and we can still see the haki trails next to him
All his dialogue makes even more clear how didn't even cared about Shanks himself, but the Red Hair Pirates as a whole coming to his ass.
Kaido already shivered during Zoro's Ashura, and he wasn't 100% paralyzed, even tho he showed to be feeling threatned
Kaido already sweated and felt scared when Luffy awakened his Devil Fruit and was sending CoC waves from the rooftop to the perfomance floor
Shanks was also extremely pissed, which shows this isn't something he does regularly, especially on a situation where Greenbull is already suppose to be in disadvantage from the very beginning, if he doesn't leave but chooses to fight everyone, he is done.
Younko fans will obviously overreact that, because the target is an Admiral, but if you bring up all the moments that suppose to work the same way for Younkous, then its not valid at all, just ignore that and pretend like everytime an Younko isn't showing to be as strong as people thought they should be (alongside their headcanons) then it's all a matter of bad writing or gag, or match-up, or bad spot, or some other shit that doesn't threatnens AT ALL the powerlevel they are in (or where people thought they were supposed to be)
