The most likely one is normal year to year variation in shooting %. Given the number of players in the league you expect a few who put up particularly good numbers over a given 3 year period. I don't rule out that the scrambley hockey the Flames have played the last few years isn't a factor though.
Buddy just stop. You are a known Flames hater. Monahan has a high shooting percentage because he's a great goal scorer. There are few players in the league you would rather have with an open chance in front of the net. There is a reason he's called 'Money-hands' and that's because he's an elite goal scorer.
Also, your comparison of Scheifele and Monahan this year is comparing a guy drafted in 2011 and a guy drafted in 2013.... As OKG has said, at the same points in their careers Monahan has been better AINEC.
Also, Peter Chiarelli, GM of the OILERS, named Sean to the initial World Cup team and said Sean will be a top six Center on that team. Scheifele made the final cut. So Chiarelli thinks Monahan is better, right now.