Maybe the books are from a time before herds were that badly affected, or else they are hushing up things that might make over-hunting look bad.
I did some research, and found sources about young elephants killing rhinos. Apparently the older males are “culled” by game control officers thus unbalancing the social order (yes, they have one) where the young bulls would accompany the older males and learn. Thus, the younger males do go into musth earlier than usual (probably a means of keeping the population up when the prime breeding males are absent) and become aggressive. They fight and kill the rhinos where the older males would ignore or let them go. I didn’t find any credible items about “raping” although there are references.
Elephant hunting is a thing of the past. Most countries where there are hunters with enough money to afford it do not allow the importation of ivory (banned in mid-80’s) so when they over populate and start to destroy crops the game departments cull them. Also poachers go after the old males with tusks.