The ~10% is what matters.
So by that argument, I can replace 90% of my food with Soylent, and get the other 10% as I normally would?
Also, how do I know I'm getting the correct mix of everything? If I go by cravings, then the stuff I'm missing is usually ice cream or cake or candy...
That 10% probably consists of candy for the kids and alcohol for the adults.
So they fed their baby candy instead of breastfeeding it?
Most experts generally agree that it's OK to stop breastfeeding your kid when they're 4 years old
Yes, my point is that people's dietary needs change. Breastfeeding is the most obvious example that nobody would deny, but there are others.
You simply can't rely on a one-size-fits-all diet without some risks. One person might be lactose intolerant, another might have nutritional deficiency, and a third might be at risk of overdose due to genetic or medical factors preventing them from offloading excess amounts of Sodium, Potassium, etc.
I don't think anyone is arguing that Soylent could replace breastfeeding (though there are plenty of people who use something similar: formula).
But for everybody else, Soylent sounds a lot easier to customize to personal needs. You can avoid allergens without losing the required nutrients, you can tune the amount of sodium and potassium to whatever you can deal with, etc. With normal food, you don't get that kind of fine-grained control.
So in my family, everyone from the 4-year-old girl to the 33-year-old man (me) eats the same food 90+% of the time, just in different amounts... and we all seem to be doing fine. Should we be dropping dead at any moment now?