What I find interesting in the discussion of Democrats vs Republicans is the assumption that a two-party system is the most effective. In our complex world, we really struggle to hold dichotomous viewpoints (as seen by the breadth of ideas in each political party).
I don't know if the assumption is that it's the most effective but rather that it's not something that will foreseeably change given the current US system.
As one political science professor colleague described it, the two major parties have a gentleman's agreement to keep only the Republicans and Democrats in power. For example, the major party candidates are automatically placed on the ballot whereas third party candidates have to jump through hoops to get on the ballot in each state. When Bernie Sanders ran for president in 2016, he ran as a Democrat even though he's actually not a Democrat. He explained that given the system, it's not viable to run outside of the two major parties. His supporters accused the party and media of trying to suppress his campaign so that Hillary, a "normal" Democrat, would get the nomination. For example, the party gave Hillary the debate questions before the debate so she'd be better prepared than Bernie.
Then there's the incestuous relationship the mainstream media, especially the Washington press, has with the two major parties. It tends to shut out any candidates it don't consider "normal," meaning a mainstream Republican or Democrat, so candidates with other viewpoints have tremendous difficulty in getting their message out. Andrew Yang, for example, noted the Washington press corp wouldn't talk to him, and he only made inroads because Joe Rogan had him on his show where his message resonated with a lot of the listeners. Yet MSNBC deliberately went out of its way to ignore his campaign, instead supporting "normal" Democrats who were polling worse than Yang.
I also wonder if a country can ever get too big for a simple democracy to work? When half of America's population disagrees with the elected incumbent and that number of people is larger than the full population of many countries around the world, is there a need to redesign the democratic approach to better represent the people?
It's probably true that a democratic system is only viable with a population that shares a common set of values. I don't think US is too big in that sense yet, but there are obvious problems with the current system.
One of the ideas behind the electoral college, for instance, was that each district would effectively choose an elector who would then vote for the president, but the states realized they could get more influence at the federal level if they wholeheartedly supported the eventual winner, which resulted in the winner-take-all method of awarding electors. This incentivizes candidates to focus on the voters in battleground states instead of appealing to most voters nationwide.
The number of House members has been fixed for a long time now. California has a population of about 40 million but only 52 representatives in Congress, so on average, each representative has about 770000 constituents. To put it another way, each person has effectively very little influence in Congress these days. The system would probably work better if it was more fine-grained, so each member had fewer people to represent.