The reason I regard this "one rifle" thing as a rather silly question is because it presumes that there is only a very limited use for a rifle.
Generalizing: .22 rimfire is best for practicing eye-finger coordination. .22 centerfires are best for varminting. 6mm through .30 work best for medium game. Big thumpers are the deal for large, hostile critters. Semi-autos work well for home defense.
No one rifle will do "all of the above" in any rational usage.
Sorry, but you're confusing calibre with firearm!
As I already pointed out, a Cape Gun SxS or O/U, a dreiling (drilling 3 barrel) or a vierling (4 barrel) gun has the versatility to accomplish killing nearly every animal in the world...That's what they were designed for! While it may not be a great wing shooting gun but say a 500/416 Krieghoff NE paired to a 16 bore shotgun with a 9.3x72Rmm bottom barrel and a 7x64mm Brenneke top barrel would easily cover the full range of huntable animals.
Many countries, states and territories in Europe had and still have laws covering firearms and the most frequent one was and still is, that there could only be one (1) firearm in the household...Add a rifle barrel to a smoothbore musket (fowler) and you have covered two different types of hunting, add a smaller barrel and you increased the versatility even more...Add a fourth barrel and even more areas are covered but I really find them ungainly...Also add a full length insert or two and the prospects get even more compl;icated.
I'll agree with you that there really isn't one "do it all" calibre even the venerable .30/06 Springfield or the newer .308 Win since they aren't really geared for the "Big Five" in Africa...W.M. Bell may have shot elephants with his 7x57mm (.275 Rigby) and Mrs. Jack O'Connor did away with a pet one with a .30/06 but they aren't allowed now by the game departments as .375 H&H or the 9.3x62/64/72R is the minimum for Cape Buffalo etc.
I saw a lovely between wars IIRC Belgium made drilling that was 2x.450/400 3¼" (.400 Jeffery) over a 7.7x57Rmm (.303 British) that would have handled Africa with ease.
Although you can gear your calibre to your environment...As long as you're not encountering "Big" bears you can get away with anything from .300 mags and preferably lower...Someone living in Northern Canada and only has moose to shoot at needs a 7.5mm and above--.300 mags, .338, .340, .348, .358...Somebody in the Southern Plains of Alberta and Montana etc. with Mule Deer and Pronghorn--really far away Mule Deer and Pronghorn--needs a flat shooting
"Beanfield style" rifle like the .257, .260, .264, .280...Someone in the hardwood forests of Eastern and North Eastern USA with 100 yds shots the norm on black bear or whitetail deer can get away with a .30 WCF or .35 Rem or even a 12 bore slug gun.