Another similar talk of the same author, earlier (2010), with some complementary information :
As for Carcharocles, officially it is widely called as such, though in Europe, it seems to have been renamed Megaselachus megalodon, as well for the other Carcharocles genus.
I am pretty sure since a while that orcas may not have preyed on Megs, at first indeed because the contemporary species, O.citonniensis, was much smaller but also that because Orcas only prey rarely on large whales, mainly juvenile and the battle takes hours. During the famous attack facing 29 Orcas against a 18 m Blue Whale, it took 5 hours of struggle for severly injure the whale.
As said above, no Orcas attack Bull Sperm Whale in Nature. So, I m highly skeptical that even modern Orcas would have tried to engage a full grown Carcharocles megalodon which is know for attack baleen and sperm whales during its time.
Fair enough, the Orcas and the smaller predatory sharks were more adapted to the new global situation in oceans.