Was he serious? That this was a Utopia? No creatives - no change allowed, because everything is already perfection. That seems to me to be an absolutely essential mistake. The whole essence of things human is that we NEVER achieve perfection. Our best efforts must embrace the possibility of change.
Parts of a 3rd century manuscript, containing fragments of Plato's Republic - wikipedia 
Looked again - it's much more complex than I remembered. Fascinated by the fact that Socrates takes the perfect polis as an ?metaphor? not quite the right concept for the just man.
The whole issue of the importance of the individual versus the social. They are such different perspectives/dimensions yet inseparable. Also is there an acknowledgement of the inevitability of entropy - the degradation from the Aristocracy to Timocracy to Oligarchy, Democracy an finally Tyranny. So that's why change is always bad if we start from perfection. But does the cycle then go in reverse?