Well said. You explained it better than I could have. A lot of those on-line universities use Kant as an introduction to ethics, so the net is filled with Kantians who argue in favor of absolutism. I spent countless hours trying to show that some principles are universal.That has been the debate for 200 years: categorical moral imperatives or utilitarianism.
I think you are correct that Mill was more effective at least in the broader realm of culture and politics. Social contract theory was right up his alley, and we can give him substantial credit for the evolution of modern western liberalism.