It's frustrating, because I've liked Hiller since I've learned about him. But even though he's lamented not giving Turcotte more ice time, he hasn't learned/become comfortable with the notion of putting younger players out there. He leans on the vets too much.
And I know you like Fiala, but I don't think 3-on-3 serves him well. While he has a lot of open ice to take advantage of, he's at his best when he has more options and to be deceptive. Especially since he does like high-risk plays, the consequences get magnified. It's why he's great on the powerplay - he has a lethal shot, can make sneaky passes, and even if there's a miscue/misfire, he has more teammates to help regain control the situation.
3-on-3 is best for players like Byfield, Kempe, Kopitar, Thomas, Foegele, and Moore (when he's healthy). These are players who do better with fewer options, but they also have speed and/or strength to generate chances. There's also little grinding/board battles, so it doesn't play to the strengths of players like Turcotte, Laferriere, Danault, etc.
But again, I think Hiller feels more comfortable with experience - compatibility with the situation be damned.