(gets out his trusty p-38 and opens this particular can of worms...)
Shot placement is only an exterior location on the animal/person
That is one way to define it.
For me, the phrase "shot placement" is not a location, it is a skillset. It is knowing what the right spot to hit
is, what it needs to be hit
with, and being able to
do it, at the desired range.
That's knowledge of the animal (the right spot) bullet construction and velocity/energy for the chosen spot and range, the skill to accurately gauge the wind drift and drop, and the eye/hand co-ordination to fire at the right moment so all these things come together properly.
Once you pass the minimum energy & penetration needed, (for the specific target & range) all that a faster, more powerful cartridge gets you is something that will allow you more of an error, and still do the job. Providing you are ok with paying the cost in recoil and other things.
IF you can compensate for a 48" drop at long range, you can compensate for a 56" drop too. That is a matter of YOUR skill, and has nothing to do with the cartridge itself.
If it was ALL about placement then everyone would be using FMJ bullets, because expansion doesn't matter if you put that bullet in the right spot.
Expanding bullets can make the "right spot" a bit bigger, but they aren't always the best choice for everything. Note that the folks who hunt big critters at close range, that have a nasty habit of trying to stomp bwana into red mush when irritated, those people tend to favor FMJ bullets. Heavily constructed solids in large calibers are the preferred choice.
The pelt hunter wants something that will not exit (ideally) or something that only leaves two small holes, not one small and one large ragged one in the pelt.
Deer/elk hunters have a much broader range of bullet designs that will work very well, but not every one is the best one for a given shot. It NEVER hurts to use a bullet built "better" than the needed, but the reverse isn't true.
High velocity, and expanding bullets work really well for almost everything. but they aren't the only way to get the job done, or the only way to get it done well. Size does matter. It may not matter as much as some people think, but it does matter.
Another thing is that you can hit two different individual animals in precisely the same place with exactly the same bullet at the same speed, and get vastly different results, sometimes. Essentially, if you don't hit the "off" button, where ever that happens to be, the critter will either do what you expect, or it won't.