I don't think Westley Richards modified the Mauser actions they used for the 318 because of any shortcomings of the '98 action itself, it was just that the 318 with heavy bullets needed a little extra room to be loaded and since 318s weren't sold on stripper clips, letting out the front ring from 12o'clock to 3o'clock allowed the sportsman to easily load from the hand.
I agree that Winchester did make a great rifle in the model 70 but remember that during the heyday of the classic English or European Mauser sporter, the American offerings were not up to the standard of the Mauser. The Winchester 54,as nice as they are, had a stamped bottom metal and trigger guard and Springfield even had to pay royalties to Mauser before WW1.
So, today, for all intents and purposes, nothing has bettered the original Mauser '98 and that is reason enough to me to hold it in such high regard.