Duvall is never going to be a big star and probably will never hold down a full time job in the big leagues, but he has brought needed power to a Giants bench that includes Joaquin Arias, Joe Panik and Ehire Adrianza who have combined for zero home runs in 286 plate appearances and Hector Sanchez who has three home runs in 168 plate appearances. Duvall is, like all those other players, a role player but he plays a different role. Duvall cannot catch or play the middle infield. He plays an adequate first base, but his real position is hitter.
The Giants were not going to play .667 baseball for the whole season, as they had through their first 63 games, but they certainly looked like a team that was too good to play .250 ball for a month. The easiest way to explain a collapse of this kind is to attribute it, in one for or another, to a change of luck and injuries. Luck and injuries certainly have played a role, but that is only part of the story.