Blind obedience to an evil idiot is NOT a Catholic virtue.
Fr. Z is himself an expert in Canon Law, he is right both canonically and morally.
Fr. Zigrang would be wrong to assent to Bp. Fiorenza's mistaken view concerning the Mosaic Covenant, which could never save men. Certainly on this matter he ought to appeal to the Holy See, since Bp. Fiorenza's opinion appears to contradict the recent declaration "Dominus Iesus".
But there was no reason for him to leave the diocese for the schismatic SSPX - certainly there is nothing wrong with the Novus Ordo which requires a dogmatic rejection of this rite legitimately promulgated and approved by the Apostolic See. And Bp. Fiorenza had given him permission to use the Tridentine for his private Masses, as well.
Watch who you call evil!
That is precisely why actual Catholics reject Lefebvre, his scandal, his crimes and his legacy.