Your first paragraph made my point exactly.
The ONLY reason a fast 40 time could lead to talk of a qb moving to another position is because that player isn't highly coveted as an NFL QB....hence, the talk about Knight, if it's legit.
So I ask you, are you saying Dobbs isn't highly coveted as an NFL QB, since he ran the second best 40 behind Knight at the Combine? Why would you be concerned that his 40 time would hurt him? Didn't hurt Mariota or Vick. Like you said, a super fast 40 can only hurt your prospects "if you're not a highly rated qb to begin with".....thought you said Dobbs was a first round talent, clearly the best qb in the draft, and would be taken no later than the 2nd round, all of which define "highly rated qb".
If Dobbs is half the QB D4h contends he is Dobbs could literally have bested John Ross in the 40 and it still wouldn't matter and the why is glaringly obvious. A legit NFL QB is worth more, by far, than any other skill position even if that person was an Olympic decathlete. People worthy of playing NFL QB don't get shipped off to catch passes from lesser QB's because the former can run faster.