> There hasn’t been a substantive change to how representatives are selected in our country in about a century,
This is false, by the way; for one significant example the gradual elimination of multimember or overlapping house districts as a means of hyper-gerrymandering for partisan and/or racial purposes (including the law finally prohibiting it entirely) was well within the last century.
> but for much of that time we were a functional democracy.
Arguably, for much of the past centry even less of a “functional democracy” than today. The combination of the structural duopoly of the electoral system and the unusually long political realignment if the 1930s-1990s where the salient political divides didn’t map to the divides between the two major parties–which produced a lot of bipartisan legislation and gets people to falsely describe it as a time of low political polarization, when it was in fact a time of very high polarization but where the polarization didn’t map well to the major parties–also meant that it was often impossible to have a meaningful voice on salient issues by voting, which contributed to considerable political violence, that really dropped as the new political alignment solidified in the last couple decades of that period.