That's why powerscaling never made sense in the first place. Shanks stopped Kaido -> Kaido stronger than Whitebeard -> Whitebeard made Blackbeard shake his boots -> Blackbeard gave a scar to Shanks
Shanks stopped Kaido -> Kaido stronger than Whitebeard -> Whitebeard made Blackbeard shake his boots -> Blackbeard gave a scar to Shanks