the tl;dr version of it is that he felt "warrior god of X" etc was a bit wordy so was trying to find a single word equivalent, but couldn't find one that fit perfectly and eventually settled on "godhead", particularly because it also ties in with the holy theme that Oda's going with re. Imu.
Okay I have found that part of the podcast. Stephen was basically focusing on the divine aspect of their title. A few interesting things he said:
- The katakana of
Nerona can be rearranged into
Kami which would mean God
. We already knew
Imu means Buddha in Kanji version. Note that the Nerona part was first revealed in the same chapter
- Gorosei's titles are basically job titles
- Given Oda's wordplay with Nerona Imu's name, Stephen was being creative with some holy terminology while translating Gorosei's titles