Asklemmy

If you just want to limit it to Haiti, Cuba, and the USSR, then yes each of those revolutions led to a vastly more humane society than the previous one. It also depends on who you're asking. Tsar Nicholas II certainly didn't see the Soviet Union as an improvement. Cuban plantation owners with dozens of slaves didn't see socialism as an improvement. There are winners and losers in history, the losing side usually isn't going to be pleased.

And who loses in a revolution? In a successful socialist revolution it's the capitalist class, colonizers, slavers, the previous bureaucracy, regional landlords. The USSR went from a backwater literal peasant kingdom to a space faring modern country within a single generation, despite a famine and despite the brutal loss of life in WW2. It's very easy to say the country that sends women to school to become nuclear engineers is not as brutally oppressive as the country with a monarch that forcefully sends women to become nuns. How do you determine oppression? Go look at things like literacy, child mortality, education, home ownership, access to clean water, and what kind of occupations women have. By those metrics, socialist revolutions typically and vastly reduce oppression.

Some have, yes, but of the ones I listed, absolutely not.

Revolution isn't an action, it's a consequence of failing and unsustainable conditions. You don't do a Revolution, it happens and you can participate in it.