The less you earn, the greater percentage of your pre-retirement income will be replaced by Social Security. It’s designed that way; to provide a higher proportional benefit to lower income Americans. You can see that in action below. Of course, the closer your earnings are to the taxable wage cap, the higher dollar amount the benefit, but the lower the replacement percentage and the more saving and investing is the individuals responsibility.
If you were earning $40,000 at retirement, your minimum replacement of 70% of income is $28,000. Of that target Social Security replaces $14,904 leaving you to generate $13,096 in annual income. To do that you need investments of about $327,400 (the traditional 4% withdrawal rule).
To meet that goal you would need to save $1,680 each year (adjusted for inflation) for forty years assuming a 6% annual return on investments. That is doable for most people and even more so if there is an employer match involved.