Expected goals

[Janik]

So is everyone successful? Or, less facetiously, has the game become more competitive as a result? Has the overall quality of baseball improved?

Also, as ad hoc points out, if this is something genuinely useful to coaches, then good luck to them. The Germans have been deep-analysing stats for the national team for 15 years now. But for me to appreciate a good performance by Germany, I don't need to know the details of all their homework.

In order:
Clearly not. It's a zero-sum game.
Probably not, now that it is widespread the chances of lesser resourced teams to use it to close gaps has ended.
Likely only marginally. The talent pool is the same, so we are only talking a few outliers who are effective with an unusual style that were completely outside the game being inside.

What it provides is an advantage over the competition if they are using more inefficient was of analysing players or tactics, like Real Baseball Men or similar. Or, equally, a disadvantage for anyone who insists on trying the outmoded ways when everyone else has got themselves up-to-date.

And as above, it isn't particularly relevant to fans. However what happened with Baseball was essentially a closed shop of conventional wisdom which needed ideas from outside gaining traction before someone inside with little to lose was going to gamble on trying them. At that point those pushing the stats had got the ear of the people they wanted, so had little need to keep badgering those to whom it was barely relevant.
Football definitely has an awful lot of conventional wisdom about what makes a difference in a game, so looks ripe for something similar.

[Janik]

All of the analytics types I know would tell you that possession is not at all useful metric.

The last-but-one English champions did so despite having the lowest average possession of all 20 teams in the league that season. If that doesn't say this is an irrelevant number, I don't know what does.

[Vicarious Thrillseeker]

It's like taking a cricket statistic and expecting it to use it to create a successful football or rugby team.

See also Liverpool's purchase of Stewart Downing and Andy Carroll based on crossing and heading stats.

[tracteurgarcon]

I'm not sure that XG for teams is that useful, although as a fan I find it more interesting than "Attempts" (which could, of course, be shots hit into Row Z from 40 yards out, or shots which just miss the goal from 12 yards), but I would think that for players it would be very useful for managers and coaches.

[Toby Gymshorts]

See also Liverpool's purchase of Stewart Downing and Andy Carroll based on crossing and heading stats.

I'd be more inclined to believe those purchases were down to shitheadedness as opposed to stats.

[blameless]

It should be noted that the gridiron team who have bought most heavily into the Moneyball ethos are the Cleveland Browns, who have won exactly once in their last 30 games and are considered a byword for how not to do things in professional sports.

It's like taking a cricket statistic and expecting it to use it to create a successful football or rugby team.

Update: it seems the Cleveland Browns' owner does not think one win from thirty is an acceptable level of achievement, and as such has jettisoned their Moneyballer-in-chief and replaced him with a more traditional gridiron guy.