Samples of one are difficult when it comes to drawing conclusions.
My Wife hunts with a 6.5x55 and a 6.5CM, both using a 140 Nos. Part. within 100 fps of each other. She has shot 2 young bull Elk, in both case the bullet penetrated both shoulders and exited, also with good terminal performance. She has done the same with several Deer but she shot one AR Whitetail that was not big at all, angling from back of the ribs to the offside shoulder and the bullet did not exit at all. I have no idea why but I do know strange things happen.
Concerning the .270 Accubond, I used that bullet on 10-12 head of Big Game with really good results but I will confess I did not shoot a Elk in the skull, or an Elk at all with that bullet. I believe it is a very good bullet.
I hope some day we have a bullet that expands at all useful velocities, Penetrates the same every time, with a good BC and very accurate, EVERY TIME. I don't know if we are there, I see new stuff like the TLR and wonder & I am thankful that the bullet companies keep trying!