That is utterly ludicrous. Cities are responsible for over 80% of this country's GDP. Small towns are dependent on wealth transfers from urban area taxpayers to rural areas. There are small towns that are diverse, but if you look at the voting patterns of those small towns, you will see white people voting Republican, and minorities almost always voting Democrat - with majority minority small towns almost always voting Democrat.
Let met let you in on something. Voters typically vote on cultural issues. Look at the blatant racism in some of the posts in this very thread. Those are not made by voters that are ultimately motivated to vote Republican because they are an ardent believer in supply side economics, they are made by voters that vote Republican because of white grievance. It's why the Republican voting base is more white and less educated today than ever before. People that live in more diverse areas tend to be less bigoted because they live in more diverse areas, and thus they tend to be Democrat voters because they are less bigoted.
You know just today, we filed our taxes, last minute, and we had to write out a $5k check to the IRS. That was on top of tens of thousands paid to the government already last year in withholdings. Why, because we are fortunate to be upper middle class in terms of income, and thus we pay a **** ton of money every year to the local, state and federal government in taxes. So you would think I would vote for Republicans, but I don't at the federal level (I do often vote for moderate Republicans at the state and local level). I don't vote for them because we have a Republican president right now that is an unrepentant racist. There are blatant racist Republican senators like Tom Cotton. There are people outside of Trump rallies that are flying Confederate flags. You have Republicans throwing a fit over the military trying to rename bases named after Confederate heroes.
I live in a fairly diverse area, I have a diverse group of friends, and I grew up in poverty around a diverse group of people, so I know that this is wrong. It's wrong having a president in 2020 that is an unrepentant racist. It's wrong in 2020 having a major political party that's damn near as white as a Klan rally and that runs on white grievance politics, so even though it would personally benefit me economically to vote for Republicans at the federal level, I can't because of what they do, what they tolerate, and what they try to appeal to - and one only has to look at the racist garbage in this thread to see what I mean.