So viewing money as tokens of value, there was just less 'value' around full stop. So having much less of it still made you relatively extremely wealthy.
Also, how much would Darcy pay for an electricity generator, an old CRT television with a PSX and all the PSX games ever made? That makes comparisons in discretionary spending difficult.
But comparing basic spending could be doable. It is, of course, easier to compare such spending for a median person than for an outlier.
Doubtless you could simply waste your money pretty much without limits (pay more unqualified people to do a bad job at building your house, for example) but it would have been much more limited in terms of how you could usefully deploy your wealth, just because there was much less of everything available.
Mr. Darcy has money, but no one will sell him the land. Flip side the selling of land and thus lose of rent was seen as an act of desperation.
Using Maddison's estimate for UK per capita GDP in 1820, suggests that the average UK resident generates more than 10.7x as much wealth now than back then.
Of course, all these comparisons are fanciful and dependent on the utility one assigns to various things. In terms of the number of servants he could employ, a man of Darcy's wealth far outpaces all but the wealthiest in the first world whereas in terms of his ability to travel to Rome expeditiously, he can't measure up to a nearly broke student.