You keep using this greeting-card explanation. It's false. Coaching matters. Game-time matters. The Spurs have lapsed in that area recently, but even they give young guys minutes for them to get up to speed an hone their skills.
And LJC tore up his knee and came back with a better game. Bertans hasn't really added new skills. If anything, he's gotten worse. He went from being Euro Durant to being Novak.
Spurs paid for his surgery. But Robertas was great before his injury and great after. The Spurs didn't make him. If anything he's another strike against stashing players.
I'm almost convinced you don't watch the NBA if you think the SPURS developed Ian. He has become a good player after 10 years in the league. After he left the Spurs after his third season, he was still a fifth big. Credit Dallas and Indy for making him a starter.
Had nothing to do with the Spurs. Players like Splitter, Pekovic, Mirotic and Saric were elite prospects who dropped because they were bound in Europe for years. Tiago became a great European player, but he would have been one anyway. Had he been American, he would have been at lottery pick (yes, everyone said it leading up to the draft).
I don't doubt they put money in. I think in general, teams are realizing that stashing players doesn't work. Unless they are already elite prospects, they are only VERY rarely becoming starters. And if they are elite prospects, they are usually worth bringing over immediately. But as far as successes on stashes, I'd say the Nuggets have the Spurs beat handily right now.