[M T]

the Efficiency stat, which measures a player's cumulative contributions to each game

I beg to differ.  At best, it combines a few aspects of their contributions into a single number.   It does not measure a player's failure to block out, or to defend, or alter shots, or occupy their best defender the entire game, or to defend their best offensive player all game, or to draw fouls, or so many other aspects of the game.   If an opponent team comes in shooting 60% on 2FGA and 40% on 3FGA and is run ragged and held to 35% and 20%, whose contribution to that is measured by this linear combination of other stats?

Despite the claim at Wikipedia, it's pretty hard to find EFF at the NBA.COM.  The link at Wikipedia to the NBA.COM's efficiency leaderboard sends you to archive.org because that old link doesn't exist any more.  It isn't in  Stats > Home. It isn't in the Stats > Players > Traditional Stats (or Advanced, Misc, Scoring, Usage, Opponent, Defense, or Estimate Advanced).   It isn't in their Stats 101 Glossary.  It isn't in the "Cume Stats".    As far as I could find, it was one column in one page at NBA.COM.

[M T]

the Efficiency stat, which measures a player's cumulative contributions to each game

I beg to differ.  At best, it combines a few aspects of their contributions into a single number.   It does not measure a player's failure to block out, or to defend, or alter shots, or occupy their best defender the entire game, or to defend their best offensive player all game, or to draw fouls, or so many other aspects of the game.   If an opponent team comes in shooting 60% on 2FGA and 40% on 3FGA and is run ragged and held to 35% and 20%, whose contribution to that is measured by this linear combination of other stats?

Despite the claim at Wikipedia, it's pretty hard to find EFF at the NBA.COM.  The link at Wikipedia to the NBA.COM's efficiency leaderboard sends you to archive.org because that old link doesn't exist any more.  It isn't in  Stats > Home. It isn't in the Stats > Players > Traditional Stats (or Advanced, Misc, Scoring, Usage, Opponent, Defense, or Estimate Advanced).   It isn't in their Stats 101 Glossary.  It isn't in the "Cume Stats".    As far as I could find, it was one column in one page at NBA.COM.