I suppose my point is more that it should be possible to identify players who you're confident will perform straight away. Obviously you can't guarantee it, but that's the same regardless of age. I was saying this yesterday; it's not asking the club to perform miracles, signing players that nobody has ever heard of for peanuts, just identifying good talent who they think are up to the task. Richarlison is an example of Brands doing it, a good young player with the potential to get much better, but who also has an impact in the short term. We've done it before with players from Lukaku to Fellaini to Cahill. Other clubs have done it better than we have over the last few years though, and it's an area I think we really need to improve on if we're going to push past that 7th/8th bracket.
For me the issue with Kean was just that right away he didn't look ready to play up front on his own in the PL. His game was quite simply not suited to what we were trying to do. It's nothing to do with coming to a new country etc (although i'm not saying that isn't an issue aswell), that was a footballing issue that we really should have been able to identify before he signed.