The issue with HPs are that you can't count on them to do the same thing every time...tissue and bone density, impact speed and maybe an slightly off constructed jacket make HPs 'unpredictable' for %100 proper expansion all the time.
Hardcast will be hardcast and act the same...they arent meant to change shape and that takes away a lot of the uncertainty...
For deer or elk its not as big of a deal...but a big pissed off bear...that is a different story