You have some merit to your question as far as power needed to cleanly kill big game at the ranges you list. 15 or even 10 years ago, you would have had more of an arguement as we were just starting to see the really premium bullets become popular for big game hunting.
I am not an overly old fella but when Istarted hunting, the Hornady Interbond and sierra gameking were pretty popular in my area of hunting. This was pretty common all around. Now yes, we had the partition and even the X bullet but both of these had issues. The partition was and is still not a good bullet for impact velocities over around 2900 fps as the partition will routinely rupture and penetration will stop dead in its tracks.
The X bullet has always had issues with pressure and limited velocity potential as well as being very finicky for accuracy.
When the larger magnum rounds starting coming onto the market, many used them with conventonal, lead core, cup jacketed bullet designs. This combination was a horrible mistake for most hunters that hunted in that zero to 300 yard range. The result was EXCESSIVE tissue damage, huge entrance woulds and sometimes huge exit wounds if the bullet penetrated that far. Very shallow penetration was a real problem and one of the main reasons why these big magnums got such a bad repuation as nothing but meat destroying machines.
Again, 15 years ago, your argument held more water. Now days, we have a selection of amazing bullets that not only hold together at closer ranges when fired out of these big magnums but they also create very little more tissue damage then a conventional bullet in a conventional chambering.
If you take a 150 gr Partition loaded to 3000 fps in a 30-06 and compare that to a 200 gr Accubond loaded to 3200 fps in a 30-06 with both fired into the front shoulder of an elk at 200 yards, about the only difference you would see is that the Accubond sustains a good permanent would channel much deeper then the Partition. There will be very little more blood shot meat if any more then that cased by the 30-06.
Now if you take a conventional cup jacketed bullet such as a gameking or Interlock or something similiar, terminal damange will be even more similiar.
Point being, if you use the correct weight and design of bullet in the RUMs, you will get very good terminal results with very little excessive tissue damage.
Back to the point you bring up, you are correct, if you put the bullet through the vitals, it does not really matter what bullet your using as long as it has the integrity to fully penetrate the vitals. The key is shot placement.
I shoot larger rifles for one simple reason, in unknown shooting conditions, you have a larger margin of error with the larger, more ballistically potent chambrerings then you do with the smaller rounds. Now do not MISREAD that statement. I said you have a larger margin of error, I did not say you need to do your very best to know the conditions dead on the money or as close as possible. That never happen however. We often get VERY close but at times we do get fooled.
With a lesser round, on those rare times we get totally fooled, you will get a complete miss or even worse a seriously wounded animal that you will loose. With a larger magnum chambering, you will likely have a 25 to 40% larger margin of error which will often mean that while you may not be right on the money, it will be close enough to get the work done still.
There have been many situations in my hunting carreer that I passed on a shot because I did not have 100% faith in a smaller chambering at the ranges and conditions I was in at the time. Over the years, I have increased the size of the chamberings I use for one main reason. These days, getting an opportunity at a good animal is pretty rare. IN my area, I may out in 20-25 days of hunting to find the one buck I want to shoot and when that chance arrives, IF it does, I want to be packing a weapon capable of taking that big game animal at any reasonable range it shows up at. If that is 100 yards, so be it, if its 900 yards so be it.
Most of the big game animals I have harvested over the past 10 years have been taken in the 400 to 700 yard range. There have been a handfull at closer ranges, a decent amount at longer ranges but most have been in this yardage window. In ideal conditions, 400 yards is just starting to get into moderate range shooting for me personally. However in some conditions, 400 yards can be out of reach for many smaller chamberings, at least it should be.
The larger chamberings do not allow you to shoot in any conditions you want but they do offer a dramatic increase in ballisitic and terminal performance that in my mind are WELL worth using one over the smaller chamberings.
I have witnessed dozens of situations where the hunter wished he had been using a larger, more powerful rifle. I have never been in a situation where a hunter took a good animal, walked up to it, found it dead and said, "I really wish I had used a smaller rifle!"
There is no such thing as being over gunned as long as you can shoot the rifle accuracy at the ranges you will be hunting out to. With todays muzzle brake designs, these large chambered rifles have MUCH less recoil then even a 270 Win with no muzzle brake. Some do not like muzzle brakes, to each their own but with todays GREAT and affordable electronic hearing protection systems, there is no real excuss to not use a muzzle brake now, especially if you use them respectfully around other shooters or onlookers. This is easy to do as well.
Just my 2 cents.
