For me, I'm looking at the percentage of "franchise QBs" (so defined as guys that a team could win a Super Bowl with as their starter) across the league, and what percentage of those guys are premium picks in the draft.  We could debate who counts and who doesn't, but I come up with around 20 guys that fit the description (I do not count anyone from the 2017 draft, nor am I including Mariota or Winston for reference).  Of those 20, only 6 come from outside the 1st round, and another 4 come from