Your original estimate is odd. The article claims that 40£ was several years of income for a laborer. If we assume 20£/year is equivalent to a day laborer, that’s around 20k$/year (in Texas, where I live, that’s a bit on the low side). That gives Darcy’s income at around 10mm£/year, in modern terms.
I mean, setting aside the ridiculousness of trying to compare economies separated by 200 years.
You're assuming that a day laborer in the UK had income and standard of living similar to a lower-income Texan in 2019. It was closer to that of a lower-income Haitian in 2019.
EDIT: I was a bit low - BoE's inflation calculator puts a £20 income in 1813 at £1,362.94 in 2018, or about the average income of a Haitian today. So let's say, a lower-income Afghan?
I'm not sure how useful the BoE calculator is for that. It's probably more useful to just look at standard of living qualitatively.
Given that a Victorian era lower-class Londoner probably looks more like a lower-class Haitian than a Texan.
I'm less sure how to compare from Austen's era, especially outside of a major city. But things like getting any medical care at all or getting enough food to eat suggests ways that poor people of that era would be disadvantaged compared to most poor people of a developed county today.
I would also caution against focusing on major cities; only around 40% of Brits lived in cities in 1811, and rural poverty was and remains even more grinding than urban poverty.
I mean, setting aside the ridiculousness of trying to compare economies separated by 200 years.