Certainly, in this era, it would be difficult to find anyone who's had the impact on both the way the game is played and the way that teams are managed than Pop. Nearly every week, you can find an article or a podcast in which someone credits a larger trend in the NBA to something that the Spurs did first or were among the earliest teams to adopt -- de-emphasizing offensive boards, emphasizing the corner 3, prioritizing 3-and-D guys, using extreme ball movement (and player movement) to break down defenses, conceding the midrange shot to limit shots from the arc, resting healthy players, to name a few.
And that's just the on-the-court stuff. It doesn't account for the culturally unique things the Spurs have used in managing the program -- drafting and stashing foreign players, giving multiple people voices in the decision-making processes, emphasizing a program rather than particular players, again just to name a few.
While it's true that a lot of people from within the Spurs organization have gone elsewhere to spread Pop's influence (and that includes some assistants who've planted those seeds in places without Spurs family head coaches, like Joe Prunty in Milwaukee, Don Newman in Washington, Jim Boylen in Chicago, Mario Elie in Orlando, and Paul Pressey with the Lakers, again to name a few) the testament to the Spurs influence is that even in places where there is no direct tie to the Spurs, teams are still trying to do what the Spurs do in a significant number of ways, both big and small.