That is true, but PSV let him go at quite a young age (19) and he made some pretty substantial steps since. Besides it isn't like the PSV academy hasn't made any mistakes in the past.

He played second tier football with NEC after relegating and became one of their best players. He showed his overall potential but was pretty inconsistent. Moved to Brugge where he made an impression and became more well rounded. Played amazingly against Atletico in the CL scoring a great goal, spiking interest. Koeman was so impressed by his skills on the wing he let him have his debut in the NT.

Groeneveld is really young and has great potential, if he keeps his development along his current trajectory he could be a decent winger for a PL club in a season or two.