Yeah, you can sit back and say "Out of those 20 prospects on average only 4 are going to do anything in the NHL" and you may be right, that's may be the average. But the thing about this Kings prospect pool is there's SO much depth. Maybe we don't have any clearly elite level prospects (I still think Turcotte, Vilardi, and Kaliyev all have a chance to be elite NHL players), but we have SO many really really good players.
There's players in the Kings pool that may not crack the Kings' top 10 prospects but would likely be in the top 5 in most other pools around the league.
I'm well aware not all of these guys are going to pan out, but I think people will be surprised how many of these kids actually do end up having NHL careers (varying in longevity and success of course, but still).
The average might be 4 out of 20 but this isn't an average prospect pool by any means. That said, you definitely might be right and there definitely might only be 4 prospects that end up making an impact in the NHL, but I really don't see that being the case given this crop of players.