4th rounders have a less than 50% chance of playing a single NHL game and less than 25% chance of playing more than 100. Furthermore, most of the time, these players take 3 or 4 years to reach the NHL.
4th rounder have value beyond drafting. look at what other players were traded for a 4th or less and ask if you would have liked these players instead. for exemple, vatrano was traded to ny for a 4th this year