There are literally like 1,000's of examples of this happening. In fact, this is the case for almost every player who goes on to be successful outside of a few elite level guys (Crosby, Ovechkin, etc.).
I mean, just on our roster - Kreider and Zibanejad were first round picks that struggled not just for 1 year, but for a few, before settling into productive NHL players (of course I'm ignoring the outlier that was Kreider's playoff success).
You might not have patience with guys who are 19 and 20, but it is extremely rare for players to step into the NHL, especially at their respective ages and light it on fire.