The difference is that MLP was targeted more this last year than Houk was because there was no Mathews/Hoffman to take the majority of the balls.
I hope that MLP continues to improve, but if you want to compare a 2017 to 2015 offense then you have to consider the players at each position. Houk was a senior and contributed accordingly. MLP will be a junior and will hopefully match Houk's performance from 2015.
I think that Trinnaman is a much better reciever than Blackmon or Juergens and if my expectations for this year are accurate he's going to explode and have a 600+ yard season.