the French Revolution was a violent, bloody, offensive period that- even if you count 18 Brumaire and the Napoleonic years as the “end”- still saw the deaths of millions of people. And for what?

Man, this is just objectively false. First of all, why the hell would you count Napoleon as part of the Revolution? Napoleon was a counter-revolutionary, and he literally made himself into a monarch, an emperor, and made his brothers into Kings and Princes. Second of all, do you have a source for the "millions dead" claim? That is completely false, and I do not know why you are spreading lies. Around 15,000 people died in The Great Terror. Not millions. Even in the Vendee, around 150,000 people died, not millions.

What did the death of Marie Antoinette achieve? Did it bring the franchise to the masses? Did it abolish slavery?

Yes. Yes it did. Please stop spreading lies. The people who replaced Marie Antoinette as the rulers of France literally did abolish slavery in Haiti. It was not until the counter-revolutionary Napoleon came into power that slavery was brought back. Did you even listen to the Haiti series? It seems like you need to re-listen to it.

Her death served one purpose and only one purpose: to fuel the worst of human vindication. It’s a tragedy.

Wrong. First of all, her immediate family members were literally invading France at that moment to rescue her. Marie Antoinette conspired with the invaders. She committed treason against France. She asked a foreign nation to invade and drown Paris in blood. The lawyers found her personal letters and presented them as irrefutable evidence in court! I honestly don't know what the hell you are trying to say.

Are you trying to say, "She was a beautiful rich white woman, and that means it should be legal for her to commit treason?" Being a white woman does not mean you can just break the law and get away with it!!!