And?
They were competant craftsmen. The skilled tradesmen used semi-skilled and unskilled workers and apprentices to support their activities, vastly multiplying their efforts.
I suspect in many cases, their actual lives depended on the quality of their work. It wasn't something they did as a hobby - it was something they did to stay alive, either through earning a living, through not being executed for sloppy work, or because they thought their god would smite them or the sun wouldn't come up if they cut corners (small pun intended)
There is no evidence of advanced technology in these sites, but there is plenty of evidence of appropriate technology.
Look at the Antikythera mechanism. No one (well, no one who knows what they are talking about) attribute this to advanced technology. It is unfreakinbelievably complex and beyond what we thought the ancient Greeks were capable of but (and this is the important bit) - but not outside of their known ability to work metal and perform complex calculations. It was the marrying of those two skills that make it stunning. I've seen this device in Athens, and it is truly amazing. I stood in jaw-dropped amazement just staring at it in the museum there.
The bottom line is your thought experiment is flawed. There is no credible evidence for ET Corn Gods (tee hee) visiting earth now or in the past. There is no evidence at all for ancient humans or anyone else "ascending" - outside of the Star Gate and Babylon 5 and Star Trek universes.
Here in the real world, things are a bit more pragmatic. People are now, and have always been, good with their hands. They make things. Clever things.
It started with fire and the wheel and got a lot more complex rapidly.
Deal with it.