Suppose we had a civilization of homo economi running programs, so that we can talk about things in terms of “computing power.” Then, at the very minimum, a central planning computer can just run those same programs, using exactly as much computing power as the entire populace did before.
Where does that central planning computer get its data?
Where does each shopkeeping homo economicus get their data? Brute force, you can still collect it all and then just send it to a central computer. Less brute force, you can exploit duplications and scaling to get the same information but cheaper. The situation is quite similar to the computing power one, and the obvious eonomicus → sapiens problems remain the same.
Where does that central planning computer get its data?
Where does each shopkeeping homo economicus get their data? Brute force, you can still collect it all and then just send it to a central computer. Less brute force, you can exploit duplications and scaling to get the same information but cheaper. The situation is quite similar to the computing power one, and the obvious eonomicus → sapiens problems remain the same.
By looking around their local environment. Homo economicus does not mean someone who has perfect information about everything in the entire system.
Besides that, homines economici each have their own goals to achieve. What goal is the central planning computer trying to achieve?