Is anybody still denying that Hakai is not the strongest attack in the series.
It's Big Mom and Kaido’s Ultimate Combo speciality. (Ha) & (Kai) taking the first half of “Haha” which means Mother in Japanese, and taking the first half of Kaido. They rely on their core (our bodies power center) to produce and transfer maximum force.
Essentially they are putting their all into it. They rely on this move when they want to send an attack beyond anything they could possibly accomplish by themselves. That is why they call it
Conqueror of the Sea.
Even just escaping it is a "very impressive" feat, they probably never ran into single person who could fully block one.
The look on their face here says it all. "Did our Hakai just... stop or are our eyes playing tricks??!"
They don't even know how, their thinking "did Luffy, Kid, Law, Zoro & Killer combined strength actually halt our attack?"