I agree with you that it depends on the athlete. Unfortunately there isn't a magic formula that works for everyone.
With Diane, she's always been very strong - her limiter was always technique and consistency, so the static start made sense. She didn't need the boost of a dynamic start to help move the bar, and the simpler the movement, the more consistent she could be and therefore the more successful both with a given lift and with the development of technical proficiency long term.
I do think starting bottom-up dynamically makes it a bit harder to be consistent with your position at the moment the bar separates as compared to starting from the top, but in any case, I suppose I would say that if you have a problem properly setting your back, you're arguably at a stage of lifting technique at which a static start is probably appropriate. I would say that I'd rather work on a lifter's flexibility than work around it with a more complicated start. However, again, it's really case-dependent and some athletes may find this helpful.
Another thought is that someone who has difficulty getting a sound back arch from the top is likely to have trouble setting a sound back arch in a squat, so I don't know that this would necessarily work for the average inflexible athlete. Definitely something that an individual would need to experiment with.