It's definitely not rudimentary. It's one of the more complex and interesting statistical measurements that uses hundreds of thousands of "events" to model probability,
and of course it's not perfect, it can't go the final step and account for "dumb luck" or "bad luck" or the mood/form/quality of the guy taking the shot or the guy trying to save it but it's pretty reliable indicator of not just quantity but quality of chance being created.
To back up it's viability just look at a league table calculated using XP (Expected points) calculated from XG/XGA in games and it pretty much reflects the traditional league table.
Nearly all top half teams slightly out perform their X/G and XGA (against) and nearly all bottom half underperform it, suggesting that better quality players make a difference.
The xg's from yesterday's games were almost identical, theirs accrued from probably double the events ours did. XG rated the biggest chance of the game Son's 2nd when clean through (0.48 xg).
"Not accounting for dumb/bad luck" or the fluctuations of players' mindset or form throughout a game is what makes it flawed...
and, dare I say it, misses half the point of why we love football.... It ISNT perfect, mistakes are. Made, and THAT'S the beauty of it... You CAN'T, nor should you be able to predict it...
It's trying to take guesswork, opinion and surprise out of the game altogether...
Xg is just a glorified video game stat generator....
Players aren't machines...
Had it been around back then, Xg wouldn't have accounted for Gerrard's slip v Chelsea, or Mendes' dissallowed goal at Old Trafford... Or Trippiers' o.g v Chelsea...
or countless other slips, brainfarts and gaffes down the years that have won or lost titles, let alone games!
At best, it's an after the event
'Woulda Coulda Shoulda' gaming app that becomes infuriating when you look back at 'what you COULD have won!
Bloody X-Box gaming generation ruining REAL football!
Football is the game it is
because of ALL ITS IMPERFECTIONS!