It makes a lot more sense if you assume Shanks was serious and divine departure was one of his strongest moves.
This is backed up by the fact that he was sweating after using FS, and the fact that Kid was also using his strongest moves against the RHP.
Shanks did to Kid with DD, what Kid was going to do to the RHP with DP.
If Kaido used yamantaka thunder bagua on the roof or if BM coated Misery in ACoC, they might have also been able to one shot Kid. But Oda intentionally made them underestimate their enemies so the allies could win.