People mentioned all of the existing similar products.
Soylent supporters said that those products are only supplements, and you could if you wanted live on mothing but Soylent. (Those people are wrong about the other products - you can live on some of them).
Now some Soylent supporters are saying "of course you wouldn't live on it. It's just for supplemental use." In which case, what advantages does Soylent have over all the other products?
Other products come in a range of flavours; you can get unflavoured versions; you can get savoury versions; you can get formulations designed for naso-gastric feeding and, importantly, they've got many dietitians and registered nutritionists working with them. (I realise that Soylent have nutritionists now.)
There are plenty of products available to you today that you could use tha do mot taste like pancake batter. They're not particularly pleasant.