I use Mealsquares instead of Soylent, but the same idea applies: it doesn't replace all meals (I only have one per day, about 400 kcal worth), but just the ones where I don't have time to make something proper. In that sense, it's strictly an improvement over what I was eating before in that situation, which was usually either going out to eat or raiding my fridge of whatever junk was handy.

If you use Soylent/Mealsquares only to replace "no-time meals", you're doing a lot better. Like you, I don't understand why someone would eat them exclusively;