I don't think they would necessarily score at a higher rate in the DEL, but not due to higher level of competition, but due to less opportunity.
If they would have stayed at their respective DEL teams, Reichel might have better numbers there than he does in the AHL because he would likely still play on his teams top line and top pp, which is incredibly rare for young players in that league. Peterka on the other hand, as talented as he is, might have had a harder time getting those same minutes and opportunities he is getting now in the AHL.
The AHL is a developmental league and the DEL is a pro league where teams, coaches and everyone else involved are always looking to win now, and are not trying to push young players by giving them big minutes. And even prospects who play decent minutes are often not on the ice when the game is on the line, in those critical situation where you have pulled your goalie trying to send the game to OT or when you are trying to hang on to a lead. That's when pretty much all teams always go to their vets.
And as
@Halfdan has mentioned most young players are only used by the clubs due to the U23 rules. I have been tracking the ice time of U23 players for the last couple of seasons, and one thing you notice, apart from U23 players too often just being dressed to staisfy the rules, but not even getting a single shift, is that even U23 players who have been doing well in limited ice time for multiple seasons will see their ice time drop, or even see themselves moved off the team entirely, once they no longer fall under the U23 since most teams would rather have a 32-year old AHL journeyman than a 24-year old home grown player.
For now the 02s seem like an aberration with several of them really doing well this season and stepping up when given the chance. Really hope they can keep this up. If Elias, Dziambor, Samanski, Szuber and Blank keep doing well, and some of the others who have shown glimpses like Stowasser, Glötzl or Rutkowski keep developing this could be big for hockey in Germany.