yes the spurs are only 18th in defensive rating at 114.6, their defensive rating when wemby is on the floor 112.5, off the floor 118.9. the lakers are 20th at 114.9, when ad is on the floor defensive rating is 114.4, off the floor 116.2.
as for why giannis won the dpoy in 19-20, they had the no.1 defense rating as a team at 102.9 and with giannis on the floor 99.6, off the floor 107.5.
17-18 is the year i'd probably make the case for ad winning dpoy. he had the stats and the best on/off impact. what i think worked against him was the pelicans only having the 14th ranked defensive rating. games played were heavily in his favor. he played 75, gobert 56, embiid 63.
i dont agree that its narrative driven but there does seem to be a push to give last years runner up a leg up if the voters feel hes worthy the next year. draymond 2nd in 15-16, dpoy 16-17. gobert 2nd 16-17, dpoy 17-18. giannis 2nd 18-19, dpoy 19-20. last year wemby 2nd. i also dont think with wemby its as much narrative as it is his status and his physical stature that enhances his case consciously or otherwise.