Sorry you don’t have complexity without planning.
You don’t planning without a planner.
A planner is is a leader. A leader is by definition is part of a hierarchy.
Find their god/gods and you will find their hierarchy.
Their religion will be the source of the lack of temples and palaces.
I suspect that the lack of temples and statues in their cities is due to laws like the Jewish religion’s prohibition of graven images.
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.