I suppose comparing Edouard and Nketiah is understandable but ultimately pointless.
Edouard, the odd goal aside, contributes very little. He hasn't progressed and still looks like a player that hasn't come to terms with the pace and intensity of the Premier League.
Nketiahs goal stats are broadly similar, but my expectation of him is that he has the ability to not only score goals but make a greater all around contribution.
Let's face it, Premier League proven goalscorers go for far more that £25-30m and wouldn't come to Palace anyway.