I average about 30g of carbohydrate and under 5g sugar for an entire day when I'm losing or maintaining my weight. 9g for a small meal (and Soylent is a small meal, it's 400 calories a bottle) is a lot, especially given that it's 34g of non-fiber carbohydrates in the bottle besides jst the sugar count..

You are eating an extremely low-carb diet that is far from the norm. The average carbohydrate consumption for a normal 2,000-calorie diet is almost ten times as much as what you're eating. So sure, I guess Soylent isn't useful for outlier diets, but it's fine for people with normal diets.