Winchester had been making .300 and .375 for years, the Model 70 had the room for a full length Magnum.
They could have had something very like the Lott or any of several .45 x 2.85" wildcats.
I've discussed this with a friend numerous times. Since the people who made the decision are long gone, we can only guess. My best guess is that, at the time, it was not a "lets make the best, most effective and efficient round we can" thing, that it was a "lets make what we can sell the most of" thing that carried the day.
It was the mid 50s, Winchester was introducing the "short" magnum (shorter than the H&H case, the only other magnum at the time), the .264 and the .338. so there is some sense in using the same basic brass for the .458.
And, while the Model 70 had the room to take an H&H length round, I think they made the .458 short enough to fit in a standard action in order to sell more. It seems to have been a rare case of a company taking a longer view than usual.
While making the length that could be fit into just about everyone's rifle didn't directly help them sell model 70s, it did make the .458 into the most popular (and most sold) cartridge in its class.
Absolutely, it was sold to the guys who always wanted an "Africa" heavy rifle, knowing they were never going to go. And, yes the marketing claimed performance that the actual round did not deliver. For the "few people" using it for dangerous game this was a serious issue, for the 98% or so of American .458 owners who never went on safari, it was much less of a concern.
There are better performing cartridges today, there were better performing cartridges
then...but the .458 Win did work, worked even better once they got the bugs out, and you could get it. Kynoch stopped making ammo for the famous African express rifles, and Winchester was making .458 ammo, so its kind of a n0-brainer, you use what you can get ammo for, even if its not as good a performer, if it still gets the job done.
But I see no point in the cartridge for North America, or even for most game in Africa.
Ok, this I can agree with, YOU see no point in the cartridge. I get that. there are lots of things (even some gun things
) that I see no point to.
Its a valid opinion, and one I understand, but tis a lot different than saying the cartridge is useless. A LOT different.
I'm never going to Africa (outside of my imagination) and I never planned to, even back when it was remotely possible for me to do it. But I wanted a .458 Win, so I could see for myself what it would, and wouldn't do.
Which is the same reason I got most of my guns in calibers I wasn't experienced with, to have them and see what they could do and wouldn't do in MY hands. Not what writers wrote about, but what I could actually do (and way before the Internet).
I was one paycheck away from having one put together in the mid 70s, had a Herter's barreled action and stock picked out (but not purchased) when I got ordered overseas, and then life got in the way of my .458 project for about 20 years...When I finally did get one, it was a real oddball .458. Found it at a gun show for a deal I couldn't pass up.
Its NOT a DGR. Someone built a lovely mountain rifle on a 1909 Argentine Mauser 98 action, fitting a nice thumbhole stock on it, and, for some unknown reason added a .458 Win Mag barrel to the less than 8lb package. Good open sights, decent trigger, drilled and tapped with bases, and a scope safety. I bought a couple hundred new brass, and my only complaint is mechanically, it could feed "slicker" (and probably would if I were using the 500gr FMJ RNs. but it does work ok with the 400gr cast and jacketed slugs I feed it.
I've run 400gr jacketed up to 2100fps, and discovered that about all the recoil I want to take, and running cast at about 1900fps is much easier on my shoulder. And the bullets still go about 2 feet deep in an elm tree (found when the tree was cut down) and that's good enough for me. Not worried about elephants though there are "buffalo" (Bison) about a mile down the road from me...I like my rifle, and I'm ok with the .458 Win cartridge, but I'm not madly passionate about it, now that I know what it is, and isn't, from personal experience.