I have no strong (or frankly, informed) opinions about the customizer or best practices for building themes - they're not my area.

However, my analytical brain tells me that there's data, and there's the interpretation of data. 24% of themes support the customizer. The interpretation suggested in the article seems to be in the area of "theme authors need to update their practices" - which suggests the response "how can they be encouraged to?". But another could be "the customizer isn't attractive enough to theme authors" - which suggests the response - "what might be wrong with the customizer?". As I say, I have no specific opinions here on the questions themselves - I'm just coming from the statistical interpretation angle.