This is because even though Jeshua ben Jehozadak would have been a high priest son of a high priest, Ezra was more righteous than he (Song of Songs Rabbah 5:2).
Emden concedes, however, that from a simple reading of the Tanakh it is evident that Jeshua ben Jehozadak was the kohen gadol, not Ezra, and that the succession was in a direct line through his male descendants for generations.
Seraiah's older brother Jehozadak was the firstborn, and it was therefore Jehozadak's son, Jeshua, who inherited the position of high priest.
20 he writes that Ezra, the first high priest, was succeeded by Jeshua ben Jehozadak.
