While Yeshayahu forewarned of the Churban Habayis he also foretold beautiful nevuos about the ultimate redemption. The word Chazon is an acronym for "Chatzi Za'am and V'Chatzi Nechama; Half anger and half consolation."
Rav Yehonoson Eibishitz in the the Ahavas Yehonoson explains that Yeshayahu's nevua spanned four Kings of Yehuda. Uziyahu, who wanted to become Kohen Gadol, and Achaz, father of Chizkiyahu, were reshaim. Yosam, the son of Uziyahu, and Chizkiyahu were tzadikim. So great was Yosam that Rabbi Shimon Bar Yochai said (Succah 45b) that if Yosam would be together with him and Elazar his son they would excuse the world from Din from the beginning of time until the end of time. Chizkyahu was a great Tzaddik who was supposed to be Moshiach but lost the opportunity when he didn't sing shira to Hashem after the miraculous destruction of Sancherev's army.
Each navi's power to prophesize good or bad depends solely on the state of the nation. Yeshayahu's nevua was good in the times of the two great Kings Chizkiyahu and Yosam and bad during the times of Uziyahu and Achaz. Chatzi Zaam Vchatzi Nechama.