I am sharing what has been shared with me, I have no direct knowledge of this.
There is more to the story than 'the 458 Lott is a bit ballistically superior due to a bit more length, plus it can fire a 458 winmag in a pinch'
The 458 winmag developed a very bad repuation in Africa.
It was originally developed as a relatively inexpensive boltgun chambering for the upper middle class American hunter going to Africa who couldn't afford a 'proper english double'. It was designed to work in a standard length action. It had some real problems. For starters:
-factory listed ballistics were for longer barrels than most hunting rifles
-even correcting for barrel length, in the real world the cartridge did not produce the velocities claimed
-very poor quality control
-the powder of the day didn't stand up very well to African weather, and weren't sufficiently tested in that environment. many powders had a tendancy to clump up.
-many reports of boxes with different powder types found in dismantled cartridges. It is unknown if this was due to simply using whatever was leftover or available, or if there was frequent powder changing due to experimenting, and somehow in the end all the loaded cartridges were gathered up and boxed, mixed. Anyways, this lead to very different shooting results from the same box
-to acheive the higher velocities in a standard length case, the powder had to be compressed. Often on the long bumpy trip to africa, or after the first cartridge was fired and big recoil is experienced, the bullet would end up pushing out, screwing with overall length and making feeding a real issue.
-Cartridge loaded to high pressures, combined with African heat, often the cartridges would not easily eject. NOT good when elephant is charging.
(some of these issues were 'dealt with' in country by Proffesional Hunters...basically the hunting guides...who would pull the bullet, dump the loaded powder, add powder they had faith in, and reseated the bullets. This lead to cartridges that were of proper length and hence would feed, and powder that wouldn't clump, AND pressures that were much less likely to cause the cartridge to bind...but this lowered real world ballistics even further. Still, a gun that goes BANG a little softer is better than a gun that isn't working)
The prevailing wisdom was that most people unable to afford the 'classics' like 450/500 Nitro Express were much better served by turning to the 40 caliber african cartridges like the 416 rigby rather than trying to us the 458 Winchester.
Many parts of this reputation are not valid any more. Powders improve and improve, now the 458 winchester is loaded to match it's claimed numbers, loaded consistantly, loaded with powders tested in african type weather, loaded with more potent powder so less compression is needed, etc.
There still seems to be the 'sticky cartridge' problem though.
so the 458 Lott must be looked at through that prism. Also note, the 460 Weatherby also has a repuation of being loaded to high enough pressures that there can be extraction issues. The 458 Lott, not only going for a longer case to get higher velocities and remove the risk of compacted powder pushing out bullets, spent a lot of time making sure pressures were such that cartridge bind was not a problem. (the big Dakota chamberings were also designed with an eye to keeping pressures low to prevent the case from binding in the action)
So while the 458 Lott lands between the 458 winchester magnum and the 460 weatherby magnum, it is considered by many people to be superior to both.
"460weatherby sticks and kicks!" is often used to point out that even some well established african sport hunters and even the professional hunters found the 458 Lott managable in recoil, but the 460 excessive, and of course, prone to bind.
It will lead you 
