I know 5 men that I've heard say that exact same thing. They would defend the 243 to the death. They no longer shoot 243s due to multiple bad experiences resulting in lost annimals. And these men can put a bullet right where they want it. A lot depends on where you are. If in a spot where you can't afford for him to run or ghost 30 to 40 yards, it matters. If it's more open and you can see him run for a ways, that's different.
I've seen a single number 1 buckshot (40) grains through the ribs kill a 220 pound 9 pt. He ran 200 yards and died. No one would have known he even hit him but the pack of dogs got to him and abruptly hushed. So we fanned out and went to where we last heard them open and there he was. There was little to no blood. Seen hogs and deer hit with one 00 or 000 through the boiler done in 40 yards. But that's not the norm. The guys around here that use the caliber do so because most of the deer shot with them make it out of the fields before they die. That way they don't have to drag or bring a tractor back to get them out of the field.
If someone wants to shoot a marginal caliber, more power to him. I've had to many calls at night from folks wanting me to bring my tracking dog. I've seen enough deer and trailed enough deer shot with them that I'm not going to do it. If I did I would be very careful about shot placement.
No one is trying to change anyone's caliber or cartridge of choice, but at the same time, many of us have had different experiences with the same cartridges but maybe with different bullet or shot placement choices.
As I have stated early in the thread, I grew up and lived/hunted in the Deep South for nearly 40 years before moving West (I still go back there and other places to hunt), and I and family/friends too hunted a lot of heavy timber, swamps, river bottoms and thickets, and I nor my son or several others had any worse issues using a 243/6mm than others using larger bores/cartridges. I have hunted with a lot of various calibers and cartridges over my decades, currently load for 52, and I have also witnessed a lot of others via my skinning poles many used. Many were good hits, some not-so-much.
I have seen numerous deer and other game hit with large calibers, small calibers, fast magnums, large-slow big bores, handguns, arrows, shotguns, etc, and many of those I shot myself. Many often fall on impact regardless of caliber, but some "regardless" of caliber or even "magnum" cartridges run several yards before dropping. Some short, some close to a hundred yards. Lung shots are notorious for this even with 12 gauge slugs or even magnum rifles, and while high shoulder shots with good bullets have much better chances of DRT, nothing is 100%.
Point being, choose a
"proper bullet" and a cartridge that will deliver enough speed at intended max impact range to expand, and the rest is up to the shooter to deliver the goods. Many trash various calibers, especially smaller than "their" imposed limits or likes, and have little to no real experience shooting those calibers/cartridges with proper and/or modern bullets designed for game hunting. Especially the heavy for caliber VLD types or monos that have really changed the game.
Not long ago, hunters, shooters, magazine writers and ballisticians were having these same discussions about any caliber under 30 cal. Bullet choices and shot placement. YMMV