Interestingly, here's each def value per according to fangraphs...
Simmons 7.1 in 55 game = .129 per game
Swanson 5.0 in 41 games = .122 per game
Pretty comparable. Swanson pretty damn good with the glove
The problem is that Simmons seemed to get to balls that Dansby can't touch and Simmons appeared to have a much stronger arm. As an example, when was the last time Dansby threw out anyone from the left field grass? My impression was that defensive metrics aren't currently as advanced as those for offense. However, I'd be happy to be wrong in undervaluing Dansby's defense as compared to Andrelton's.