There's a huge difference between a vertically integrated company competing for customers and vendors and the entire economy of a country, IMO. One evidence is that large companies keep ossifying and failing to adapt all the time which means the economy needs more than one giant company to move forward. A new Google needs a way to tell the state/the giant computer/whatever, "you're wrong, search works badly and we can do better." It's very hard to do that if the giant computer is running everything and effectively decides what you do (and it cannot run the economy if it cannot decide who does what, or at least what projects are funded and which aren't.)

Also the USSR didn't just have problems optimizing supply chains. It had a problem deciding what to make. You couldn't buy woolen sweaters so you bought woolen socks and made sweaters from the woolen threads making up the sock (yes, I fucking participated in this fuckery). How is a giant neural network going to figure out how many socks and sweaters people want better than demand affecting prices affecting production, even if I grant you the assumption that the problem of managing the socks supply chain is nailed today?