It's important to recognize the fact that what radio plays and what people buy and/or stream do not necessarily align.
You have songs like "According To You" and "Daylight" that did very well on radio without the sales or streams to justify that.
You have songs like "Gangnam Style" and "Skyscraper" and "We Can't Stop" that did very well otherwise but stalled on radio.
There are many examples of songs not performing as well as could be expected from their pre-single performance as well.
Ke$ha's "Blah Blah Blah" featuring 3OH!3 was No 1 on iTunes upon album release, and 3OH!3 was popular at the time. But despite the fact that it followed the monster hit "TiK ToK" it still stalled on the radio.
Rihanna's "California King Bed" was the fan favourite, so was Britney Spears's "Criminal", yet both flopped as singles.
Taylor Swift's "Sparks Fly" did go No 1 on the radio in the end, but with poor overall sales and little impact, despite it being a massive fan favourite, from a huge era, and it hitting No 1 on iTunes upon release.
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On country radio, there are numerous more examples.
"Red Solo Cup" and "Girl Crush" and "Not Ready To Make Nice" all sold very well, but didn't do nearly as well on country radio.
On the other hand, there are loads of songs that went No 1 on country radio with dismal sales and streams.
Carrie's own "Wasted" and "So Small" spent 3 weeks at No 1, and they did not sell as well as 1-week No 1s "Last Name", "Cowboy Casanova", or "Undo It". "I Told You So" sold so much it went Top 10 on the Hot 100, and it couldn't even go No 1 on Hot Country Songs. "Something In The Water" performed very well too, as shown by its dominance on Hot Country Songs and the gospel chart, but it didn't even go Top 2 on the radio.
Of course the fact that it didn't shoot up to Top 20 on iTunes after the ACM performance means it probably isn't going to be a mega sales and streaming hit without a viral video, but it really doesn't say anything about its radio potential.
For all we know, "Southbound" could've tested very well with radio, or at least the best among all the remaining tracks. It doesn't need to lift her career to a different level, it only really needs to continue her status as a hit-maker. She has already achieved so much, with moderate hits here and there she will certainly be considered a legend in another 10 years (but would be more difficult if she just flops from this point on).
