> By this definition, the USA are a third world country then.

Not even close

Looking at the poorest places, yes, absolutely.

Chicago

https://www.youtube.com/watch?v=BNbGnPyFi8k

https://www.youtube.com/watch?v=mUQGiquHPgs

Greenville Mississippi

https://www.youtube.com/watch?v=V2SPHSCa-6Q

Now look at Oaxaca and Chiapas where people build their houses from stacked cinderblocks and take home plant clippings for fuel to cook dinner from their job as a gardener.

And more importantly compare the pay and purchasing power and the school systems. I don't think Americans realize how little Mexicans make and how expensive everything is to them except for labor.

None of those are examples of the third world

You just have not seen structural poverty at the state level

all the roads still work, there’s services, access to schools, technology (mines), property rights

So many riches that people of the first world take for granted

There is certainly a lot of inequality in the USA, but Mexico and other Central and South American nations take it to yet another extreme.