I'll cede your point on the level of sophistication, but I'd say this is actually pretty damn impressive. Drainage projects like this would have been a large community effort. Cars and computers are probably less intensive given modern infrastructure, especially when you consider that everyone involved in the car making likely has been specialized in the field, whereas those making the drainage system in the stone age were exactly not that.

I don't know that I would say this particular thing is evidence that anarchism is the best system, but I'd say it's a thing to point to when discussing it. Assuming some kind of left wing utopia in the future, I don't think anarchism or statist Marxism is the only way forward. I think it will highly depend on the area. Densely populated urban areas likely will need some form state, rural areas could probably function pretty well off of an anarchist model. Computer networks could allow for decentralized planning, allowing for a sort of hybrid model that increases liberty, prevents the concentration of power in a few individuals, while giving us more of an anarchistic (or at least syndicalist) model hybrid with the benefits of centralized control.

Yeah, in 1850, ,1900, 1930, I'd say Anarchism was the clear preferential option. Today, I am an anarchist, but I think we'd be foolish to ignore the lessons of the USSR, Cuba, even China, and the major advancements in technology that could allow for a interconnected society that could enable decentralized control of the economy.