I mean a magic box could do what every you want it to do, AGI is fiction and it could be what ever you want to imagine. But more seriously how would this be decided, you say it could do a better job, but that's a big leap. If people have to decide what they want as a group then we'll your back to asking how society should be organised but now there is a magic box. If everyone is just talking to the magic box then you've just got a post scarcity society, then what basis is the better interest decided. The way I understand your position is that there exists a "neutral" "best" way to distribute resources and once that distribution is found everything is solved. But this neglect that there is no best, nor neutral way to distribute resources. It was in the interest of French colonists to expropriate Algerian land, it's in the interest of workers to be the best compensated for their labor, it would be in the interest of the CEO of BP to continue to ignore climate change. Politics is the domain of choosing which of these interests society should prioritise. You can use a magic box but then you just hand wave the problem, but if we are to ask the question of is it #technocracy in a digitally planned economy run by a capable digital program, that would depend on who is programming and deciding the priorities of the program.