The Spurs were not going to Draft Chandler Parson's since they just Drafted Kawhi Leonard even though Parson's has better than Kawhi. Kawhi is the better Defender and the better fit in the Spurs System and to be completely honest a real perimeter defender since Bowen.
Isaiah Thomas is 5 foot 9 Point guard passed on by the entire league playing for one of the Worst teams in the league producing inflated numbers. The Kings had even traded for Jimmer Ferdette in the lottery in 2011.
The Spurs do not simply fit apples to apples. The Spurs have holistic view of their team, which is why certain players flourish and others do not. Look at some of the players who were amazing in SA then left to become Duds. GameTime: Popovich's Coaching Tree | NBA.com