1) No that is hockey. And I'm not sure you understand what I'm getting at.
The best way to predict guys who don't have goals against is guys without shots against.
That's why we care about shots, because their predictive nature to goals.
2) NHL hockey rules and relationships we observe exist in the environment that is present. You can't compare other non-NHL levels. Heck, in only as far down as CHL, Corsi is much, much weaker and goal differentials are much, much stronger due to the differences in environment.
It will be even more extreme for level like beer league.
3) Corsi isn't possession. Possession and Corsi are different, as are shots. Possession with the absence of shots and opportunity to score does not create a shot event. You can see this in the extremes, like in soccer, which has far more dead possession time. It has a relationship, but it is not the same as Corsi. What Corsi is is a goal differential predictor.
4) I bemoan +/- for more reasons than just it being about goals. I bemoan it because it sucks.
* It is a raw +/- with no context of rates or TOI, so +5/-3 is same as +305/-303
* It includes empty nets, pp -s, and pk +s
It's a ****** stat. If you want to use goals, use even strength goal% (goals for/[goals against + goals against]). It is sensitive to TOI differences, and doesn't have the stupid PP/PK/EmptyNet rules. It still requires about 3-4 years to stabalize for players, but it's better.