The only fat that would be any more melted would be the parts that are more well done, medium rare is the same temperature.
And doing long cooked meats that are traditionally braised and keeping them at medium or medium rare is heaven. Medium rare short ribs that are just as tender but more juicy is to die for.
Also, I feel sous vide steak has more flavor because it’s literally cooking on its own juices, if you sear/cook/sear you are getting all of the seared flavors literally cooked into the meat