This is largely true however there have been historical great strides of change largely thanks to congress such as Civil Rights, the New Deal, Abolition, and Healthcare.
While Republicans supported Abolition, and initially supported Civil Rights and Healthcare; they abandoned socializing Healthcare and dragged their feet on it while gaining more popularity for supporting Traditional Marriage and illegalizing Abortion. These brought them into direct conflict with Civil Rights (which was a bi-partisan effort in the end) but they unconvincingly tried to say their platforms merely defending Religious Freedom which finally backfired on them this year.
Not that I’m saying Democrats have always been on the right side of history. At one point, staunch opponents of Abolition and Civil Rights while being fierce proponents of Segregation.
The difference is that most Democrats have not continued championing these failed constructs 50 years after they lost.