Logically speaking. There are 31 teams in the NHL which mean there are 93 available 1st line spots around the league.
Obviously who plays as a first line player constantly fluctuates as players decline, retire, get injured and aren't the same etc. Not to mention that just because you play on the first line for one team doesn't mean you are of that caliber. Just as some teams have 2nd line players that would be 1st line caliber on most teams. So we'll call it approximately 70-80 top line caliber players in the league.
Any given draft you probably will have 5-12 true top line talents. They aren't always going to be the guys picked top 20. See players like Kucherov or Gaudreau. For example the 2013 draft IMO only has 3 true 1st line guys MacK, Barkov and Monahan. A bunch of tweeners like Lindholm, Drouin, Domi etc. There was also a top pairing dman in Jones.
So statistically speaking most of the guys drafted are probably more likely to end up 2nd line caliber guys or lower than top line guys. It's tough to predict outside of the can't miss guys who will hit that top end skill and who won't.