Sure can have complexity without a central planner.
What is needed are a few simple rules people know to follow.
Essentially, things like the rule of law and property rights.
Planning does not require a single ruler or a tiny ruling class.
Sure it does.
You don’t have the rule of law without someone to write those laws and someone to enforce them.
An orderly city doesn’t arise organically from a few simple rules voluntarily followed by those choosing to build there.
Drive around Pittsburg if you want to visit such a city that grows organically. You will never be more lost in your life.
Drive around in Salt Lake City if you want to drive in a well planned city that was laid out from the beginning to be orderly.
Humans are genetically wired to be led. People chose their leaders or their leaders chose themselves.
Either way, for good or ill they will be led.
All of history says it is so.