Kingman's errors only told half the story. You generally have to reach a ball to make an error on it. His errors didn't even take into account the balls he couldn't reach. He had no confidence going back on a ball, so he would position himself practically on the edge of the warning track, allowing plenty of would be outs to drop in front of him. He had very limited lateral range, so the center fielder would have to shade several steps towards Kingman, which opened up the right center field gap for countless doubles and triples. Add to all this the fact that Kingman played in the artificial turf era, and the fact that equally inept (on defense) Bobby Murcer was in right field and you had a major problem on your hands with outfield defense.
Kingman could hit those bombs, however. When we would take charter bus trips to Wrigley in the late seventies our driver always had us there in plenty of time to watch BP. And the adults, who would normally head for the bars until game time, would go in early and watch as well when Kingman was in the house.