I feel like a broken record, but a few things worth keeping in mind:
Nobody was there when JBR was attacked, and nobody knows how hard, fast, or what trajectory JBR's head wound was inflicted with. Human skulls also have sutures and weak spots, and we have no idea if JBR had other prior head wounds other than the golf club under her eye.
I don't think the demonstration was to create an exact reenactment since that would be impossible. I think the point of the demonstration was to show audiences that yes, it is possible for a little boy to crack the skull of a young child in a similar manner resulting in a similar head wound.
The team of experts probably knew that if they were to present the BDI theory, that viewers would have to see it for themselves. IMO