It's my understanding, aside from the Lott-Cape Buffalo story, that Win, in order to reach marketable velocity numbers for the 458 WM in standard barrel length rifles, had to compress a type of ball powder that did not react well to the combination of heat and compression over time. There are several reported instances of early 458 WM factory ammo giving "squib like" performance in the field. I have no first hand proof myself, but these reports came from different, independent sources. I think with modern, temperature insensitive powders available now or by avoiding certain types of powders, there should be no reason to expect squib loads in the 458 WM. Likewise, I think the factory loaded ammo issues were also corrected early on.
I fully understand about questioning the "need" for a 458 boomer that may never be used in the field. One thing about it though…. there is something about going to the range once in a while and absolutely knowing you have fired a rifle! The only downside (s) (that I can think of) with the Lott (or similar) vs the WM are: cycling and bullet choice. With a properly set up bolt gun the Lott will cycle fine in a standard long mag action designed for the "regular" 3.6 inch mag category cartridge. However I can notice (feel) the difference in cycling the longer cartridge- not a lot of difference but there is some. The other thing about the Lott, Watts and Express is the crimp groove on many 500 (510) gr bullets is not placed correctly for these longer length cartridges in a standard mag rifle designed for the 3.6 inch cartridge. (I believe it is a good idea, when reloading these heavy recoilers, to crimp firmly in the groove.) I have become convinced that many if not most of the 500 (510) gr bullets on the market have a crimp groove correctly placed for the shorter WM OAL and not for the longer carts. I discovered, good news if reloading for the longer rounds, is that many of the .458 450 and 480 gr "Nitro" bullets do have the crimp groove in the correct place for the long cartridges like the Lott.
Bottom line- if you want to push a 500 (510) gr bullet to say the factory quoted 2050 fps, the WM will have to be pushed to a higher pressure than the longer Lott, Watts or Express. Range time with a chronograph and researching pressure data will reveal the truth. The longer Lott or similar cartridges aren't even breathing hard to get to 2050 fps. Loading to lower pressures, leaves a lot more margin for error if the gun and/or ammo is used in high temps.