Mana and alii ranking or caste was not the same thing. Kamehameha I's bloodline/genealogy/mana was less than his own children by Keōpūolani who was just about the highest ranking alii of her time. Kamehameha I's children from her had a higher ranking than him in many reliable sources and the story says that Kamehameha would let the children play on his chest while he laid on the ground to symbolize their higher mana from mother who was of higher ranking than Kamehameha. I believe sources refer to Lunalilo as being the highest ranking alii of his time but...of course, he lived past Kam IV and V to have a sort rule. Maybe "his own time" was that year.