I actually don't think any of these qualify as worst leaders of their civilization. Nikolai II was the clueless and out-of-touch heir of much worse tsars like Alexander III. His cluelessness abetted the revolution, but the revolution was coming anyway. (If anything, Alexandra Feodrovna's anti-Russian obtuseness and gullibility was far more culpable.) Similarly, Louis XVI was clueless and out-of-touch but by no means the worst monarch France ever had; it would have taken a far more savvy politician to stem the tide of the French Revolution. (I'd also add that Marie Antoinette has been vilified beyond all reason. The people liked her, the nobility hated her, and then the Revolution happened at which time she became guilty simply for being queen. People invented wild conspiracy theories about her in the wake of the Revolution, but in reality she was a spoiled, not particularly clever child who was completely unprepared to navigate the trials of the French Revolution. And she most certainly never said, "Let them eat cake," an anecdote that was related while she was still a little girl in Austria.) Charles I was a bad king, no question, but I don't think he even bears comparison to, say, George IV or Stephen of Blois. Basically, all of these leaders except Nero have in common being murdered, but for at least Nikolai II and Louis XVI these were the results of forces far beyond their control. (Charles I was certainly the author of his own undoing, but I'd still maintain he's not the
worst England has had.)
So here are my suggestions for alternatives to the civs you listed:
Alexander III - Russia: Reversing virtually all of the reforms his father Alexander II reluctantly made, Alexander III basically paved the way for his son to be murdered by revolutionaries. Alexander II is perhaps given too much credit for his reforms--he basically made them out of well-justified paranoia--but they were a step in the right direction. Alexander III dragged Russia back to the Middle Ages, and the backlash that manifested in the October Revolution was the inevitable result of his reactionary policies. Nikolai II certainly deserves to be blamed for being so incredibly out-of-touch that he had no clue what storm was brewing under his feet, but that storm was set in motion by Alexander III.
France: I'm going to restrict myself to post-Carolingian France (ruling out the very obvious candidate Louis V
the Do-nothing). I don't have any one candidate here, but some names I'd put forward would include Charles VI (his reign started out promising, but mental illness took its toll on his reign), any of Catherine de Medici's sons (Francis II died as a child; Charles IX ignored his mother's more temperate policies and instituted rigorous persecution of the Huguenots, died young, and paved the way for the end of his dynasty; and Henri III was probably the best of the three but inherited a weak throne after forfeiting the Polish throne and, once again, died young), and Louis-Philippe "the Citizen King," who combined all of the cluelessness of Nikolai II with positive ineptitude. (I restrict myself to kings--otherwise I think there's little doubt France's
worst leader would be Philippe Pétain.)
Rome: Take your pick of any of the litany of emperors whose reigns lasted a few months before they were assassinated and replaced by another military puppet.
England: Charles I isn't a bad choice. He was an able enough ruler, but absolutely senseless to the political realities of the time in which he lived. His competence makes me inclined to pick someone else, though. George I couldn't even speak English. George IV was an intelligent but lazy fop who was more interested in the affairs of the royal bedchamber than affairs of state. Edward VI was a sickly child whose affairs were run by competing ministers. Lady Jane Grey barely lasted a week. Stephen of Blois was weak and indecisive. The much-beloved Richard the Lionheart barely spent six months in his own kingdom and bankrupted it with his crusade, leaving his brother John to take the fall for his own mismanagement. Plenty of candidates here.
Some other ideas:
James "history will vindicate me" Buchanan of the United States.
Montezuma II of Aztecs (oh, wait--we've had him...more than once)
Isaac II Angelos of Byzantium
Tutankhamun of Egypt
Hui of Jin of China
Abdulaziz of the Ottoman Empire
Philip II of the Netherlands
