Is he 50k better than Rendon or Bregman?
He's expensive because he's looking like one of the cards that will remain price locked to complete mlb collection. Anyone who wants Mantle will have to over pay for a few cards.
As far as card performance, no, he's not 50k better. However, his card price may go up so you might want to bite the bullet now and buy him if you ever plan on trying to get Mantle and Sheffield
To add onto @EvylShaun the price will also hold because of the Ottavino card for the Rockies collection.