If your main event is still voidwatch (or any other event where 300% tp aftermath is kept up with little sacrifice to weaponskill damage and accuracy is capped):
99calad>99rag>95calad>95rag>90calad>OAT>85calad>Borealis
If you use your drk in other events where keeping 300% tp aftermath is more annoying:
99rag>95rag>99calad>OAT>90calad>Borealis
Also worth noting that war sub plus fighters roll and an optimal tp set (one with plenty of multiattack) substantially hurts OAT great sword as an option.
Wat
Ragnarok 99 and Ragnarok 95 will both beat Caladbolg 99 in Voidwatch.
Caladbolg 90 will also not beat OAT, even if the OAT has to have fighter's roll (which honestly, if you have an OAT/mythic DD run something other than fighters)