As has been said, he was injured for a 10 game stretch where he put up very little points.
I'm not too concerned about Bastian's development. For whatever reason, bigger forwards like him just never seem to put up the same point totals as the smaller, skilled guys. Just look at Zacha, Simmonds, Jeff Carter, and I'm sure there are other cases. The guys that do usually end up being your elite talents like Benn; Bastian is still along a similar path to Simmonds right now.
Bastian's the type of player where I would say looking at the player is far more important than watching the numbers, especially at the junior level.
Big guys take a bit to develop, but Zacha was dominating the OHL in his post draft year. He had 77 points in 58 games between regular season and playoffs. Simmonds was comfortably over a PPG in his post draft year (89 points in 74 games). Carter was comfortably over a PPG.
People make this false equivalence between the NHL and OHL, that a guy who is a big body / checker / defensively sound in juniors automatically will be that way in the NHL. It doesn't work like that.
Putting up points in juniors is a sign of your basic overall skills, not just offensive/point producing skills. Skating, hockey sense, stickhandling, etc. Those are all extremely valuable tools in the defensive zone as well as the offensive zone, so a forward who is struggling to put up points in junior likely won't ever make it to the NHL in any capacity.
None of this says Bastian won't continue to develop and become an NHL player. But my money is on him getting another year in the OHL followed by a significant amount of time in the AHL.