About 55 years ago I spent many hours and days on end with my Aunt and Uncle who were big country music fans and they would play "CFGM 1310 Country Radio" pretty much every waking minute. At that time there was a distinction between styles that was unmistakable.
Steel guitar, fiddle, acoustic guitar, and harmonica where the mainstay instruments and twangy sultry voices singing ballads and catchy dance tunes were the norm. I think they still contain those key ingredients but the stage presence and musical content has been beefed up...that's what I see and hear...
In the early 90s I was engaged to a girl who loved country music (and horses) and I reacquainted myself with the music. There was still quite a distinction at that time too...so it was somewhere between then and now that there has been a bigger shift towards what we have today.
I have to admit that I have not been paying attention but did notice lately that the music wasn't as pure and simple as it used to be...but I'm not much of a music critic other than I know what I want to hear...and that can vary between Orchestras playing symphony classics to the latest acapella cover of Hallelujah by Pentatonix...
I found this article online that sort of gives a quick overview of the evolution of country music...I found it after I wrote the above personal perspective to see how much I was out of touch...lol.
http://www.theo2.co.uk/news/detail/how-country-music-has-changed-over-the-years