Markets are optimal but capitalism is not. If you let supply and demand set prices but don't allow extracting value you get an economy that is both fair and efficient. The rule is all profits must be reinvested or paid out to workers and the state can impose price controls if margins are too high.

Yugoslavia tried it and they had the best economy from the eastern bloc growing faster than a lot of the west. China and Vietnam went further in their reforms and allowed private investment but they still kept state owned corporations instead of privatizing everything, and they don't worship markets and property like America does.

I don't think it's an accident that all these mixed economies got ahead of pure socialist or capitalist systems.

Ah, the familiar twinge of sorrow and rue at reading the name "Yugoslavia"...

Do you have any source defending your point better than you can in small comment ? I am interested but a bit unconvinced so far