I quite like Erwin as a player/Rangers WUM, and I reckon he'll do pretty well for Killie, but I'm not particularly bothered that we're missing out on him. He's potentially a marginally better option than Bowman or Fisher but not by enough to justify signing a 4th striker who's pretty similar to the ones we already have.
In retrospect, Erwin to Leeds might be one of the best pieces of business we've done in years. We lost a raw player who had one decent season at this level in return for Louis Moult and a six figure profit.