"More expensive per Calorie" is not necessarily "more expensive" for the target audience. The classic "2000 Calories per day" assumes some level of physical activity. If you don't have any physical activity, you're better off consuming fewer Calories per day, as long as you get all the other nutrients you need.

This is an important consideration. The target audience of Soylent likely has some wild variation in desired caloric intake, perhaps 4-6x between people who want to drop some pounds and people who lift as a hobby.

Yeah. The creator of Soylent makes a point of saying that it should be tuned for the person using it. Hopefully in the long-term they'll offer versions with varying calorie content. Alternatively, they could offer a two-component system with nutrients and minimal calories in one and pure calories in the other, to make it easy to tune that one variable for your target calorie consumption.