I never understood how Hakstol got labelled as a development coach. Has to be just because he coached college for 10+ years.
When Hakstol left North Dakota, there were a few articles and interviews with the Hawks top players, and all of them said that under Brad Berry, everyone knew what they were supposed to do. Some of them even said, (paraphrasing) "when you made a mistake under Hakstol, he would just yell at you, but with Berry, he teaches you what you did wrong and helps you learn what to do in the future". They all basically said that they were more confused and the communication was not as clear when Hakstol was head coach.
He surely did not show an ability to connect with the young players in Philly, and I have never read any young player praising him for his teaching and communication, which is the foundation for development coaches.
Then we had most of the young players in Seattle publicly saying that they were often unclear what was being asked of them or what they were exactly supposed to do on the ice.
Beniers is one young player that seems to have came in and done fairly well under Hakstol, but he has had professional level coaching for a long time, playing years in the USNT program, and then playing a couple of years under Mel Pearson at Michigan. He was definitely far more prepared than most junior players are going to be entering the league (and possibly a lot of AHL players). which probably made a huge difference.