I am in agreement with your call for additional research. Oronsaye himself was motivated to do his research and write his book based on some concerns he had with Egharevba. Before he died he DID collect vast amounts of material on the Ogiso era but was unable to write it before he was called to the great beyond. Hopefully his family will let someone else access to his vast files so that his work may be continued.
However, I must correct a misattribution in your posting.
You stated that “With due respect to Chief Egharevba, an example is his assertion that Ikaladeran was defeated in Ughoton in a battle with the forces of his father Ogiso’s Ewodo. This is hard for me to believe, because there is no trace in Ughoton as to where Ikaladeran died. “
On pages 2 & 3 of his book (A Short History of Benin – 4th edition) Egharevba does NOT say that Ekaladerhan was either defeated or killed in the battle with forces of his father. I quote:
“….the Ogiso banished Ekaladerhan with his mother from the city instead of killing him, and Ekaladerhan eventually became the founder or the village of Ughoton (Gwatto) on the bank of a river after a long course of wandering in the forest……………..Three years after the banishment of Ekaladerhan, the Ogiso’s wives still remained barren and so the Ogiso sent two men and two women to consult the oracle once more through the same diviner. The Oracle declared Esagho to be the cause of the barrenness of the women…………After this, the Ogiso hastily despatched messengers to Ughoton to beg his son to return to the City with
the messengers and overlook the treatment he had suffered. But Ekaladerhan, complying with the advice of an old woman there, refused to return. The Ogiso sent troops repeatedly to bring Ekaladerhan but Ekaladerhan dug pits into which the troops fell and perished.
Consequently, the elders, who had intended to make Ekaladerhan Ogiso after the death of his father, now gave up the intention on account of the soldiers he had killed in the pits……….”
From that point in the book, until he addresses the issue of Evian (page 5) and the coming of Oranmiyan (page 6) Egharevba was SILENT on the fate of Ekaladerhan – an omission which Oronsaye addressed in his book.