Nothing new under the sun. Take a look at Central Park in New York. Almost everything you is is constructed. They dug the ponds and built up the hills. They didn't have geofoam but if they did they would have used it. Look a Tunnel View in Yosemite. It's there because NPS manages the trees below the view to frame it. Hell, the very idea that there is urban space and nature space is something we humans invented.
I think you're not replying to the main (or at least, most important imo) point of the parent: it's that this man-made landscape has now plastic embedded in it, with all the potential risks it entails
For what it's worth, I don't think there's anything wrong with creating (or re-creating) natural spaces. There's no reason to become a nihilist over it.
