XR were nothing like Marathon Winter.
Grip and rolling resistance weren't target properties; long life was.
Their place in life was for use by transcontinenal tourists, riding things like UK to Oz, or Barrow to Ushuaia, where they may end up doing several thousand miles on gravel roads, and didn't want their tyres to decide to wear out in the middle of nowhere.
My pair have done about 2500 miles, about half of which was on gravel (including Tibet, where, at the time, tarmac was limited to the Lhasa to airport road (pre tunnel), about 10 miles either side of Xigatsu, and actually inside anything else that may qualify as a town). The state of wear is "lost most of the flashing".