I have a feeling the four finger and thumb over the top of the slide, is a technique that became more prevalent with the rise in popularity of autoloaders.
This method is probably most useful for those with limited hand strength.
Most old school autos have some type of grippy area near the end of the slide for the older school slingshot method.
For me, it is faster and more intuitive for my weak-hand to load the fresh magazine and slide right back into the shooting position, while my trigger finger (which is already straight along the frame) simply swipes down on the slide catch/release.
To load the magazine, then go weak-hand over slide, or slingshot, then back into the shooting hold, takes a little bit more time.
Bottom line, use what works best for you. Lots of people have different abilities and limitations.
