I don't understand the connection made here, because calculating the quantum state is NP-hard and is very time consuming, the object cannot exist in the universe? How is that preventing the macroscopic system from existing? How does the complexity class have anything to do with the real world?
For example, a shortest path problem in the real world does not have any use for complexity theory: http://www.johnmurray.io/log/2012/07/10/Real-World-Shortest-...