Using absolute chord analysis instead of relative chords (i.e. roman numeral analysis) doesn't make sense. As others have noted, the original dataset is flawed because the structure of a song is critical, you cannot omit repeating chords. Programmers/analysts should take more care to understand music theory or the underlying field at hand, before compiling datasets or doing analysis.

"Most common chord" is mildly interesting, but not really that useful. The most common key, and the most commonly used chords relative to that key (i.e. with roman numeral analysis) would be much more useful and interesting. This would help paint a clearer distinction between e.g. country and jazz, not that "jazz uses Bb major more". Also, anyone with general instrument knowledge would surmise that since Bb and Eb instruments are much more prevalent.

"If you’re sitting down to write a song, throw a 7th chord in. The ghost of a jazz great will smile on you."

7ths don't belong to jazz only, and the average songwriter isn't making data-driven decisions on how to settle on the chord structure for their song.