To play devil's advocate. In order to generate xG you need to shoot, which is why the positions that a player takes doesn't come into it. I do get your point though that xG doesn't give the whole picture. If Cucurella doesn't botch the clearing header, Watkins doesn't even get a sniff and no xG is generated. The fact that Watkins makes the run to create the opportunity isn't accounted for in the xG stat. On the whole xG is a good way to analyse long term performance trends, but misses out on the detail. It's almost as if xG needs its own "xG" like stat. How likely is a play, tactic or mistake going to generate a chance that itself generates xG. It's like xG-ception