If McGonagall were alive today he would have made a fortune writing country songs...

Not so - he was always straining for the grandiloquent and high-flown (and missing it every time). That's the reverse of what country music songwriters do.

In both cases the result can be bathos, but for very different reasons.(With McGonagall it's invariably bathos, with country music more often than not it escapes falling into the trap.)

One possible flaw in the methodology of the research - they seem to have based it on the number of hours put out by local radio, rather than on the listening figures. Those might well amount to the same thing, but not necessarily. And as has been pointed out "country music" can mean a whole lot of different things.