Love that the stats crowd can't get their head around one of their favourite measurement stats not actually providing insight into a game of football.
Possession is only going to be insightful towards outcome if all other things are equal*. That is to say, if you have the majority of possession, but never try to score, you will not win a single game. Even if your possession is 100%. The stat these people really need is percentage per possession percent of actually trying to go something.
Or they could use their eyes.
* If one side takes risks with the ball, and tries to score**, and another side doesn't***, the outcomes will likely be quite different for the same possession, and same quality level.
** ie traditional English football.
*** ie this turgid Spanish dancing crap that the commercial corruption of football, in favour of protecting a small number of brands, has lumbered us with.