Soylent is like birth control for food: it lets you choose whether food is going to be for pleasure or for sustenance. I eat it often because it's healthy, quick, and I actually enjoy it. That said, I also very much enjoy food with family and friends. They're too completely different things though, but previously we had to use the same tools for both needs.
I believe the point is that a sandwich doesn't have the macronutrient ratio most people want and a full range of micronutrients so people don't have to be worried about missing anything important if they decide to eat sandwiches for 2/3rds of their meals.
Isn't Soylent equivalent to a supplement in essence? It's a base diffused with certain nutrients. Why is this different than a sandwich and a vitamin in terms of nutrition? Or even more, how is it different from a vitamin?
A focus on fat in the morning, then vinegar in the afternoon and finally umami in the evening would serve me well. All between 2 pieces of appropriate bread.