Not sure I agree with this. Spurs probably should be aiming to sign ready-made players to kick on and win something, but Pochetino still seems to like projects that he can mould into his system. Jansen and Wanyama were both signed last summer and neither are the finished article, but have still made a solid number of appearances this season.
I would prefer he stayed in Germany, but if he did fancy a move to the PL, Spurs would probably be the best option to develop his game and give him reasonable game time. He's certainly the type of player Spurs could do with as a plan B, though they may opt for someone more proven.