It's probably not healthful in any meaningful way but it is "better for you" than many of the so-called healthful alternatives out there.
The Kombucha at 12g of sugar per 8 fluid ounces is low in the overall scheme. Vita Coco (so called wonder drink) has 11g per 8 fluid ounces. Only the strictest Kombuchas (GT's) have significantly less sugar per 8 fluid ounces (2g to 4g, depending on blend).