I have a few thoughts
1. Agree, he may be higher percentage shooter, however even then it's hard to consistently shoot over ~12-13%.
2. The next coach likely increases shot volume thus mitigating regression. Also add in a bit of development time for a young pro.
3. Sam had 9 goals with 23 shots in 20 games in his end of season stint with the Ducks. Let's say next season he can average 1.5 shots per game
4. 1.5 shots per game over 82 games is 123 shots, with a 13% shooting percentage you get 16 goals.
15+ goals is still great over the course of a season. I think expecting him to be a lock to hit 20 next season sets him up for failure. I think 15ish goals in a 3rd line role and some 2nd PP time is about right. Also hopefully he generates more assists next year.