A chief isn't a king, oga isn't a king,
Yorubas had a title similar to "king" but if you ask the average yoruba in modern day Nigeria to name a yoruba king they cannot. The average yoruba in Nigeria doesn't know anything about yoruba history. The same way the average Igbo in Igboland does not care about Igbo history, hell you'll get looked at weird for trying to talk to them about the Kingdom of Nri, they haven't fully grasped the idea of writing down and repeating knowledge. Being able to read and write effectively is still a privilege in Nigeria.
You have such limited knowledge, but you are writing like you are knowledgeable about some shyt.
Mansas are Kings/Emperors.
Mansa
Mansa is a Mandinka word meaning "king of kings" or "emperor". It is particularly associated with the Keita Dynasty of the Mali Empire, which dominated West Africa from the thirteenth to the fifthteenth century. Powers of the mansa included the right to dispense justice and to monopolize trade, particularly in gold. Mansa Sundiata was the first to assume the title of mansa, which was passed down through the Keita line with few interruptions well into the 15th century. Other notable mansas include his son Wali Keita and the powerful Mansa Musa, whose hajj helped define a new direction for the Empire. The succession of the Mali Empire is primarily known through Tunisian historian ibn Khaldun's History of the Berbers.
What does Mansa mean?
Chiefs are not kings. Chiefs are actually more like noblemen.. Chiefs report to Kings/Mansas/Emperors. An African Chief is the same as an English Earl or a Marquis..
Earl - Wikipedia
By the way I am pretty sure that an average Yoruba Nigerian would know that their word for King was Oba.
Oba is the word for King in the Yoruba | Sola Rey