Not really sure where the narrative of his shot being bad came from, I suspect it was his low goal totals.
Here is what HockeyProspect.com said about his shot in their draft guide.
"The final area to breakdown regarding Stützle skill-set is his release. He’s not an instinctive shooter and you could make an argument that he underutilizes his release, which is a contributing factor to his lower goal scoring output this season relative to his assist totals. That said, don’t mistake his low scoring total for a prospect who doesn’t have the ability to shoot the puck. Stützle has the mechanics necessary to be an impact scorer at the NHL-level. The most notable aspects of his release point are in regards to his footwork and his coordination within his shot. The footwork allows him to generate additional velocity by gaining inside positioning on his release point, as well as masking the specific point of the release. "