Imo:
Less adept/inclined to use the media to his advantage as others like Montgomery, Bradley or Patton.
Also less blunt in using political interference and manipulating Eisenhower to get his way than any of them.
The army group didn't take part in most of the fighting in Normandy or the Falaise pocket.
Nearly half of the formation were foreign (French) units including a lot with "inferior" backgrounds (not only the Germans were racist).
The last stages of the war saw the army group move into secondary areas (Austria, Northern Italy) as compared to the high profile leaders who rolled into Germany itself.
It wasn't the largest army group, it didn't fight the highest profile engagements, it's leader wasn't in the spotlight of...