I don't think you can make an effective argument even diving into counties. Without context you can't look at a county map and make an evaluation based on that information. Sure the big picture of, that's a big urban county and that's a big rural county will work but it fails at the why portion of the question.
Colorado was mentioned early on with that statement that 3/4s of the state wanted to be Republican but the Front Range Megalopolis decides which way the state will go. I think that's actually a fallacy.
Demographically Colorado has 64 counties and a relatively low population (5,773,714 based on the 2020 census, all the population numbers are based on the 2020 census). Historically there is a division between Western Slope (counties west of the continental divide) and the East (often referred to as the Front Range, but it includes everything from the Divide to the border with Kansas).
Make no mistake Colorado is big, 8th largest state in the US yet the majority of the population is concentrated in the area between Fort Collins in the north and Pueblo in the south. Looking at a map will quickly show why this is and why there is such a division between Western Slope and Front Range.
But its not that simple, and a statement saying the 3/4s of Colorado voted or wants to be Republican cannot be taken at face value.
Let's dive into the numbers:
64 Counties, in the 2020 election 26 voted Democrat and 36 voted Republican (3/4 quarters would have been 48).
The population is widely spread out. The three largest counties; El Paso, Denver & Arapahoe have a total population of 2,100,987 (36% of the total population). The three smallest counties: Mineral, Hinsdale & San Juan have a total population of 2,358 (4% of the total population). Democrats won 2 out of the 3 largest population centers and Republicans won 2 out of the 3 smallest.
Based on that its easy to say urban vs rural but it paints a very incomplete picture. 18 Counties are considered Western Slope, 4 Counties straddle the divide and the other 42 are Front Range/Plains counties. Of those only 14 are truly just plains counties and the rest run down the Front Range or have a portion of their county included in that area. Pueblo and El Paso are good examples of this with the major population center on the Front Range and almost all the rest of the county being plains.
And then you look at a red and blue map and it doesn't split nice and even, western slope to front range/plains. The expectation would be that the majority of the western slope would be Republican. The actual result was a split; 9 Western Slope Counties voted Democrat, 9 voted Republican. of the 4 counties that split the line, those also split evenly; 2 Democrat, 2 Republican. Which meant that the real "showdown" occurred in the 42 Front Range/Plains counties. Of these the Democrats only won 15 counties, but those 15 counties included 7 out of the top 11 population centers (counties with a population of 100,000+) including spots 2-6. The total population for those top 11 counties is 4,748,414 (82% of the state's entire population). Of that total the 7 counties won by the Democrats amounts to 3,331,060 to the Republican amount of 1,573,057.
Based on populations Democrats won more than 50% of the vote and did it in both rural and urban areas.
All this points to is the fact that you can't look at a map of a state's counties and make an informed decision on why. Based on a map Colorado should be Republican they won more counties, but population is the key to all of it and whether we like it or not urban populations are going to make the difference.
Looking at Colorado it is certainly not true that 3/4s of the state either by county or by population wanted to be Republican. And since rural and urban are tied at the hip splitting one off from the other will have both fail, you literally can't have one without the other and to try and separate them would only invite disaster.
There are a lot of factors that play into all of this just looking at a map of a state's counties isn't going to provide the answer.
