Does reviling the unjust ruler fall under the hadith "Reviling a Muslim is a Fusuq (disobedience)"? And does that diminish a person's good deeds if he has not experienced direct injustice from this ruler?

Cursing a just Muslim is not permissible, and its perpetrator deserves to be disciplined. As for one who is not among the people of justice, such as a profligate or an oppressor, it is permissible to curse him with a word that corresponds to his action, such as saying: "O profligate," or "O oppressor." However, it is not permissible to curse him with something that is unlawful in nature, such as declaring him an infidel or lying about him.