The wildcat 7mm - 08 developed a stellar reputation for accuracy before it was standardized by Remington. And gun companies like to introduce new chamberings that will generate sales for buyers after the Latest and Greatest.
There is about as much difference between the 7mm - 08 and 7x57 as there is between the .243 Win and the 6 mm Remington. The former are based on the 308 case and the latter on the 57 mm length Mauser case. The Mauser case has a longer neck and slightly more capacity. But the boxy 308 case may burn powder more consistently.
They are similar in performance, and both much easier on you than than a 7 mm Rem Mag.
And, at least one professional ivory hunter killed a lot of elephants with a 7x57.