The article mentions carbon dating but they don't say what it was that they chose to carbon date to obtain the dates they report.
Stonehenge has its "Aubrey Holes," which harken back to a time when what stood there was wooden rather than the stone that survives there today.
Were there any similar holes containing vestiges of wooden structures at Ales Stenar? The article simply doesn't say.
After the visit and seeing and climbing the very large earth pyramid I used the sun to plot an east west line in my driveway. Knowing that, I laid out a perpendicular and had a perfect north south line. It is easy. Once you have the cardinal points, determining the equinoxes and the solstice becomes easy.
Monks Mound is laid out precisely in alignment with the cardinal points. From the Woodhenge center pole looking east the alignment of the mound south edge is barely to the right of the top edge of the mound. It marks the summer solstice sunrise. It misses the edge by an angle representing the latitude!
Cahokia is readily available........ go! PS: At the time Cahokia was larger than London and most european cities. Greater Cahokia was estimated to be 25,000 people