Where you live in TN, I'm sure that's true and for anyone in an area that only has edge, I wouldn't recommend T-mobile, unless they are using only a feature phone and the edge coverage is good.
I won't deny that T-mobile is an urban carrier, and has a smaller network than other other big 3 carriers. But it works well for many people like me and they have more than 152 customers, let's not be absurd they have like 8 or 9 million I think.
But your statement needed to be qualified, they don't have ZERO 4G coverage, their 4G coverage where I live in Central NJ is very good and I get 6 - 14 mbps on T-mobile.
No one has the original definition of 4G, that's LTE advanced. LTE might be a little closer than HSPA+ , but they both produce comparable data speeds and have been declared 4G. I agree people still arguing that hspa+ isn't 4G and lte is need to give it up, your living in the past.