Gasol has Randolph playing on the same lineup, and has managed to play very well, and earn lots of minutes. If Splitter were that good, believe me, they would have given him more minutes and yes even taken some minutes away from Duncan because they still want to preserve him. And Duncan played the least minutes of his career last year. There's no excuse Jose. Kawhi started off on the bench, but his great play basically forced the Spurs to give him more minutes.
I'm not saying Splitter completely sucks, but he's as good as he's going to get. And again, Gasol had the skills when he got drafted. He just adjusted to the NBA game. Splitter doesn't have those skills, and at 27 I doubt he will be "developed" into something else.