Marxism-Leninism is literally the study of how to overthrow capitalism. So you can go ahead and try the Paris Commune again for the dozenth time but yes. It is the alternative to capitalism.

If you want to overthrow capitalism you're going to be a ML or you're going to try to start over from 0 for entirely stupid reasons.

Those concessions to social democrats were made when the USSR was presenting an alternative, workers were presenting an alternative (dragging the boss out and beating him to death infront of his family), or both.

People forget FDR was a Roosevelt, old money. His predecessor had just sent the tanks in to raze an encampment of insurrectionist soldiers within sight of the capitol building. FDR didn't give concessions because he secretly thought his class deserved less and the workers deserved more, but as a means to protect capitalism (and his privilege under capitalism), and nearly got coup'd for doing that.

When the bourgeoisie don't have a reason to fear the guillotine, they stop buying guillotine insurance and your social democracy gets hollowed out by neoliberalism.