There are so many angles with bullet weight, bullet diameter, sectional density, and energy. There are arguments from smart people explaining how each are more important than the other.
I was talking with a buddy the other day about this. We recovered two 33cal 210gr partitions from elk that my dad killed and a 30cal 180 grand slam from an elk I shot. The old grand slam with two sections like a partition and A-frame.
All three of those lost about 40% of their weight. We all know the performance of the mono bullets. A bad one retains 95% of it's weight.
By that math when the bullet has stopped you go from 210gr to 126gr in the partition style bullet with the 33cal and 180gr to 108gr with the 30cal. On that same note if I'm shooting a 120gr mono bullet out of a 25cal it's 118.75gr when it's done.
When anyone talks about big game bullets they are talking about penetration, expansion, and weight retention.
Common sense leads me to we could all use a hell of a lot less rifle by going away from lead and get the exact same results. A 7-08 with a 140gr etip, GMX, TSX, etc. should have the same realistic killing ability as a 250gr lead bullet if fired at an acceptable FPS.