Use enough gun, but not too much. Is that the answer?
I think it is, it's just not a very precise answer. "Use the gun that's right for you , and for the hunting you do" would be my take on it - doesn't pin it down much better, really, does it?
The logical conclusion of saying there is no such thing as too much gun, and that the hitting power of larger magnum calibres can compensate for less than adequate shot placement, is that we should all be using artillery rounds. That way, even if our shot placement was off by a couple of yards, we should still have adequate stoppping power.
Clearly that is nonsense. Even the magnum brigade don't suggest using 50BMG or artillery rounds on deer, so they obviously do accept the concept of too much gun - they just set the bar a bit higher in terms of calibre than I would.
Now, if someone says to me that they prefer to use a 7mm or 300 Mag on deer, and if they can shoot it accurately, I will say to them "de gustibus non est disputandum"* and happily accept it. The problem I have is with people who CAN'T shoot these calibres properly but still insist on using them. There are plenty of reasons why people would do that: bigger must be better, it's macho to use a magnum, more power can't hurt, the salesman/gun magazine told them they needed one, plus the whole collateral damage argument. And it makes a REALLY BIG BANG when it goes off, so perhaps if I just point it in approximately the right direction the deer will drop with fright.
Here's a thing I've noticed, here in the UK. Over the last few years, sound moderators have become widely used on deer rifles. Guess what? People who have fitted them say they improve accuracy. By reducing the report (and to a large extent the recoil) of their full bore rifles to something approximating a .22 rimfire, they are finding them gentler to shoot and thus shooting much better. That's true even at the lower end of the calibre spectrum, down at the .243 end of things. There is a culture shock effect from using a sound moderator, however. The rifle doesn't SOUND powerful enough to kill a deer. Thankfully, ballistics are unaffected.
There is a conclusion to all this, and here it is: recoil and muzzle blast affect everyone's field shooting, perhaps to a greater degree than they would recognize or acknowledge. Deer are not particularly difficult to kill, and magnum power is not essential to do the task. Bullet placement is key, and for most people this is facilitated by using a rifle which doesn't kick hard or boom too loudly.
Use enough gun, but not too much. And enough gun might be less than you think.
* To save you looking it up:
De gustibus non est disputandum - There's no arguing matters of taste