McDonald's food contains a larger variety of foods and nutrients than Soylent. For example, a Big Mac has all of the following:

Beef, Salt, Black Pepper, Bleached Wheat Flour, Malted Barley Flour, Canola Oil, Soybean Oil, Pickles, Egg Yolks, Onion Powder, Mustard Seed, Vegetable Protein, Turmeric, Lettuce, Onions

It's also loaded with HFCS and a laundry list of preservatives and additives. I'm not saying it's the healthiest food, but given a choice between the two, I'd choose the one that at least has a few real food components.

And before you mention Supersize Me and the effects it had on his health, remember that it was an n=1 study and The Fathead Movie did the same experiment and his health improved.