I also tried to evaluate this claim that households have less real income after debt service. It is difficult because it depends on many nuances, like whether we care about all credit, or simply revolving credit. Your graph is interesting but difficult to interpret - the % change per annum is declining, but that's reasoning from some higher order derivative. I looked up a few more data series.

https://fred.stlouisfed.org/series/BOGZ1FL153166006Q - consumer credit indeed rises from 1984 to present, but from ~17% to a peak of ~25% to the present ~22%. This seems to be more than adequately compensated by real household income growth over the same period. Even if we take the peak value of ~25% that leaves real household income after subtracting consumer credit higher than in 1984. But note that this series isn't debt service payments, it's credit stock. It doesn't make much sense to subtract. Unfortunately we don't have consumer credit payments going back this far.

https://fred.stlouisfed.org/graph/?id=TDSP%2CMDSP%2CCDSP%2CF... - it is difficult to find debt service payments going back to 1980. Interestingly the measures relating to debt service payments appear to be basically flat or even slightly negative over this time period, though the consumer debt service series only goes back to 2005.

So to my eyes it is difficult to support the notion that income-minus-debt-service has deflated over the past fifty years. I also find it difficult to take this data and state the stronger conclusion that half the population requires consumer debt to afford basic necessities but some fraction did not 50 years ago. The median appears to be better off.