Is “Deposing the elder in favor of the younger and the Quanrong sacking Haojing” true?
attested in history
The Records of the Grand Historian, 'Annals of Zhou', records that King You of Zhou deposed Queen Shen and Crown Prince Yijiu, made Bao Si his queen and Bofu his crown prince, which provoked the Marquis of Shen to lead the Quanrong to sack Haojing, killing King You and Bofu. The historical novel follows the historical facts.
Bofu
Zhou Youwang and Bao Si's son, the official history records that his appointment as crown prince triggered the Quanrong to sack Haojing, and the novel basically follows this.