I think it's important to clarify which Bergers do what...their hunting rounds with thicker jackets behave a bit differently than say a 215 hybrid, hell even a 230 hybrid behaves a bit differently than a 215 hybrid.
Broz, who was a big part of popularizing hunting with 215 hybrids believes it is due to the longer bearing surface on the 230's which limits the dead space between the nose of the bullet and where the lead starts, which I believe is a bit longer on the 215's than the 230's.
Very similar concept to the Hornady ELDM vs ELDX but the reasoning for the Berger Hybrid vs the former is that the thin jacket actually performs better without a "ballistic tip" than with, at least that is one of the better researched educated guesses.
I went away from the Bergers for several years, one because they were hard to find and another because the good idea fairy said that high-velocity closer shots on elk sized game might do better with a bonded bullet like an accubond, but after a couple of seasons with results that weren't that spectacular on whitetail I am back to the Hybrids and life is good. Comparably, I have never seen more devastation on an animal than I have with the Hybrids.