Because draft year production is usually what makes a kid get the rankings he gets? Who in the history of any draft did you see kids get 80 plus points at draft year and it didn't reflect on their draft selection? Aside from much smaller players? Like Corey Locke. Who also happened to be really slow.
Usually a mirage production is based on either you are just a good junior player (see the same Locke). Or you are solely a product of. Mind you, I'm not going to advocate that Sennecke was solely a product of Ritchie. Way too easy to do that. I think they fed of each other. But the jump in points, aside from getting used to his body could also be explained by pairing both guys with each other. Please note that it could also be the explanation for Iginla rise..him playing with Cristall. And yes, Iginla ALSO was a big time riser.
But no, there are no other concerns for Sennecke than the ones you named. There's a PDS post-draft syndrom that we all have and we now think everybody will take the tangent of Galchy/JK/. We shouldn't do that.
Again, I won't have Sennecke as my top 5. Yet, if I'm a scout, have access to him, to his entourage, to the specialists as far as where his body can end up to be, there is NO DOUBT that he has the size, the speed, the IQ, the scoring touch to be a top end prospect. The tangibles are there. But D+1, no matter those, you have to wish to see a big jump in stats no matter how you see that.