Not many will want to hear it, if you loaded him up some Berger bullet. It would be a game changer in the performance of deer. The mono bullet will zip through a deer. The Berger may not even exit dumping all the energy in to the deer.You're correct. But they are accurate factory loads so that's what he was using. Worked fine on his Oryx hunt and on safari, just doesn't work well for deer too close. Too much of a good thing.
Mono bullets are good for heavy animals that can make the bullet expand. For lighter game cup and core bullets will perform better from my experience.