For example if we use the current equation for a possession using last years numbers.
*All per game league averages
pts per game = 96.3 FGA = 81.4 FTA = 16.9 TO = 14.6 OREB = 11.4
So what we currently get is 96.3/[81.4 + 16.9(0.47) + 14.6 - 11.4] = 1.04 pts per possession
Using the equation I offered we get 96.3/[81.4 + 16.9(0.47) + 14.6 = 0.93 pts per possession
So the league currently averages 104 pts per 100 possessions. Using the equation I offered we get 93 pts per 100 possessions. You can ofcourse do the above and calculate each individual teams average possessions, rebounds per possession, assists per possession etc etc etc. Then compare against the league or another team etc.
Its the same method, with a different equation and therefore different results. So one can still get per possessional efficiency, its just going to be different than what it currently is. (each action per possession will on average be less valuable than how its currently calculated)
I'd argue that accuracy is more revealing than convience. Personally I think measuring the equation by using -OREB is definetely more convient. 1) its always been that way, so continually measuring it that way is convient (especially when comparing against historic numbers). 2) it makes possession equal (in any given game) which makes it easier to compare at a game level.
BUT, if its less accurate than thats not really an excuse. Or atleast shouldn't be. It would be an absolute ton of work to go back and 'correct' old data - yet if we can make that work more accurate, its benificial in the long run
Bold 2 - I'm not saying its necessarily better (I mean I DO think it is, but thinking it is and it being so are two different things). What I really want to know is why does a possession need to be considered over only when the ball changes hands as opposed to when the shooting team gives up control? Or why is that a more reasonable way to value it? It seems rather arbitrary when we consider the rules of the NBA. Its not illogical, after all in most sports we consider a possession over when the ball changes hands. But NBA basketball, with its unique limit on how long one can control the ball (ie. the shot clock) may demand a different view.
Both equations I provided are simple measure of the number of possessions. The say nothing other than 'how do we measure a possession'. But this is also what all box score stats are derived from - its from here they get the estimated value of any actions. So if the average number of possessions per game changes, it will definetely effect the value of all statistics in a game. (as I showed by pts/possession)
Bold 3 - I kind of addressed this already, but it most definetely will effect how each individual players action is valued. Without going into too much detail, how rebounds and missed shots are measured are signficantly different, resulting in much different values (it is one of, if not the, greatest inconsistency between metrics). This would completely alter how PER or WP goes about measuring those particular statistics. I can go into alot more detail into that, but it would have to be extensive and so I don't want to do that without you (or anyone) interested in a more extensive explanation.