Based on your comment about 'almost no bearing on the occurrence of a double hit', it seems that you say a straight shot on a close ball has the same chance of a double hit as a very thin cut on that same ball, given the same stroke. This does not feel at all correct to me. The difference in the likelihood of a double hit at 42 degrees of cut versus 48 degrees of cut would be much closer. But again, I can't see how you would say 'almost no bearing'. The vectors suggest otherwise, clearances and all .... If you are speaking of only the 45 degrees of elevation rule, you comment may be correct, but the rule has two options.
In a more perfect world the education would help, but I think the rule is to make the game less confrontational in these situations. If all games were refereed then the rule would be unnecessary.
I believe that the chance of a double hit increases as the CB and OB get closer. I also believe that calling some double hits is difficult (hence the guidelines for calling said infraction). Double hits take the form of 'obvious' through 'very subtle'. So, to make the game more reasonable when playing without a referee, the 45 degree rule is used. Does it make illegal hits legal ? Perhaps in some situations, but at least the ruling is clear and applies to both players. If the balls are a bit farther apart than a chalk cube, the opponent can call a foul. If the shooter disagrees, then we go to another thread and argue it there
Dave