I think most relevant to next year, would be the comparison of how Sr Qb's did that did not play in the NFL.
We don't have an NFL QB on our hands. So to look purely at stats comparing BYU's past QB factory to the NFL and suggest that this implies Riley will do well is somewhat misleading.
Covey and Feterik are your best comparisons really.
Furthermore, the original thread that began this conversation said nothing about 'returning' starters. It was a simple statement about SR Qb's. Which are a very inconvenient truth for your point I realize.