They were not heavily suprised or shocked or scared anything there.
And they don't even know one person stopped it, they are thinking all 5 top SN stopped it, but ofcourse no one can full block it anyways. That is why Big Mom said very impressive/not bad, just for them escaping it.
I guarantee you that until we see Big Mom and Kaido team up together again, or another Yonkou level characters with AP like them, team up for an ultimate combo, we will not see a move as devastating as hakai.
Dude a single admiral can f**king destroy an island easily do you expect two yonkos doing their best cannot destroys.
Most of Hakai went up to sky, if it was directed down at the island it will be disintegrated like nothing.It's the strongest attack in the series.
Ha Kai is Big Mom name and Kaido name put together, there will be no greater combo of Big Mom and Kaido together displayed in Wano. There will be no greater move than the ultimate combo of two Yonkous together. That is why Zoro paid a high price for blocking it.