While I don't have it in front of me, I believe Ed McGivern used the tip of the finger (meaning the pad on the end of the finger, right where the instructor was referring to) for his shooting and I'm certain he tried it every way possible. So there just might be something to that. However, there is more to the story than that.
It is not commonly mentioned that some people's physical characteristics make them a potentially better shot than other people. That statement may border on the politically incorrect but there are some laws that cannot be repealed. People with certain characteristics have an advantage in shooting, just like they do in football. In general, people with short arms will shoot better, at least for target shooting, than people with long arms, all other things being equal. It should go without saying that people with better eyesight should shoot better, too. Also, a stronger person should be able to shoot better, especially handguns, than a weaker person, at least if they have stronger arms and hands. Of course, it doesn't mean they will. Just like a tall person just might make a better basketball player than one who is a foot shorter.
In any event, it would be more accurate to say that some people have the advantage over other people.
With pistols and revolvers, all the action takes place in the hand. But not everyone's hands are the same. I guess manufacturers are aware of this because clearly an S&W model 36 and all the other I and J frame revolvers were intended to be used by women and children, judging by the size of the grip, while Colt single actions were intended to be used by men missing the little finger. I myself have relatively long fingers (all my relatives do), so for me to use just the tip of my finger, or the last joint, so to speak, does not work on a lot of handguns. But that is also why custom grips are popular, especially for target shooting, which is what used to be adapting the gun. This is easier to do for some guns than others, especially for automatics. Some more recent models have interchangable backstaps or inserts (or whatever you call them). Some target handguns, which of recent years has usually been an automatic, have very elaborate grips, to the extent that you could not holster them, at least with a normal practical holster, whatever that might be. Such modifications are not found to the extent on target rifles but you get to use two hands on a rifle.
You are probably aware that the original Colt 1911 was modified because some hands came up a little short, so to speak, when it came to grasping the pistol. And, judging from photographs of other people holding a Colt .45, they were justified in the modifications that resulted in the 1911A1. Then, there came a time when people thought that the thumb had no place in the grip but at this point we leave the original story.
Elmer Keith said you had to work it out for yourself. So there!
