Not everyone has an assortment of rifles,like golf clubs,to select one for any task.
Its entirely reasonable (some would say "normal") for a person to have one centerfire rifle.The "hunting rifle" . For a whole lot of folks,the battery is a .22,a shotgun,and a big game rifle.
IMO,maybe up into the 80's and 90's,I'd venture that was typical.
Rifle selection was somewhat regional,but without hard and fast rules.For many folks who hunted in the woods,"Deer Rifle" meant something with a lever.
Yet there is no denying the DCM Springfields,P-17's,etc,and the "sporter" changed folks idea what a hunting rifle was. And sure,the commercial makers were there,too.
What was true then,is true today.
For any big game hunting that needed doing,at least in North America,if you showed up with a 30-06,you showed up with the "right" gun.
Of course,it was necked up and down. 25-06 to 35 Whelen.And,there were Mausers.The 7x57,gave us the 6mmrem,and 257 R.The 8mm,no slouch.6.5x55,too.
Then there were the 30-06 "equivalent" cartridges,with 30-06 the standard..300 Savage,and 308,and all the derivatives.
All of those pretty much defined the standard,and all will slap down game animals.
I started as a teen in the late 60's with a 7mm Rem Magnum.I walked into the gun store to buy a .270.The one in the store had a feed problem,so I left with the 7mm.
Of course,that became my new standard.At some point,20 some years ago,I decided I wanted less messy kills.I went to the 257 AI.I shot better,it was enough,it killed really well.But I had a larger rifle for elk.
I don't hunt much anymore.Some things,my body is done with.If I build more hunting rifles,I'll likely have my Grandkids in mind.I have mine to give them.
But,maybe.....The idea of a light,elegant 6.5 Grendel on a Howa is appealing.
IMO,that cartridge qualifies well.I'll probably pass my AR's on to them,but I'll lean them toward a bolt gun for hunting.My predudice.
I don't use a .223 on big game. I have other choices.IMO,its marginal,has limitations.That does not mean I criticize anyone for using it.
I have seen irresponsible shooting,with associated wounding/suffering,with big,belted cartridges.It is not the cartridge that does it.
If I were giving advice,my predudiced opinion would suggest .250Savage,.243,260,6.5 Grendel ,as good cartridges to select.I would give them a nod
If you choose to hunt with your AR-15,etc,in .223..if you do your part,you can make it work,but,IMO,its not ideal.I would give it a shrug.
For perspective,a .357 Mag handgun or a .45 cal roundball muzzle loader are regarded as adequate for deer hunting.
With a proper bullet,the .223 AR willcreate more wound channel,and potentially can be fired with more precision.