This argument isn't clear cut. I would take an elite WR over a toolsy average QB any day. IMO an elite WR is taking you farther than guys like Jay Cutler or Ryan Tanehill.
Except he's not. An elite WR isn't taking you anywhere without a QB. Guys like Larry Fitzgerald and Calvin Johnson couldn't stop their teams from sucking. Jay Cutler and Ryan Tannehill are going to do more for a team than an elite WR. That's simply the nature of today's NFL. The QB position is that valuable and the WR position is that unvaluable.
I think Ramsey's post sheds alot of light on this debate. Elite QBs who can cary a team to the superbowl are rarely found outside of the top 6 in terms of first round QBs. In fact 2nd round guys have been more successful on average. If a QB is there at 15 that says alot about him according to draft history the success rate is low recently.
Current starting QBs that led their team to at least one Super Bowl:
Tom Brady - 6th round
Russell Wilson - 3rd round
Ben Roethlisberger - 1st round (#11)
Aaron Rodgers - 1st round (#24)
Peyton Manning - 1st round (#1)
Eli Manning - 1st round (#1)
Joe Flacco - 1st round (#18)
Drew Brees - 2nd round
(I know Peyton is retired but I'm counting him because the 2016 regular season hasn't started yet)
So no, your statement isn't accurate that they are rarely found outside of the top 6.
As for your contention that QBs drafted in the mid-first round have a low success rate, that's also untrue. Since 2000, there have been 8 QBs drafted between pick #11 and #20. There's a 50% success rate (4 out of 8). In the last decade (since 2006), the success rate is 40%. The success rate of QBs drafted in the top 10 since 2000 is 54% and in the last decade, it's 50%. So there's a higher success rate with top 10 QBs (not surprising) but it's not a significant difference.
On the other hand, the success rate with second round QBs over the past decade is 27%. Since 2000, the success rate of 2nd round QBs is 28%. I was also very lenient with second round QBs. I classified Osweiler and Kaepernick as successes when I would not have classified either as successes if they were drafted in the first round. Removing them, that number drops from 27% and 28% to 13% and 17%.
So no, second round guys have not been more successful on average and lasting to pick #15 does not mean a guy is going to bust because there must be something wrong with him. If that logic were to hold, then there would have to be REALLY something wrong with a guy for him to last to the 2nd round.
If the goal is a superbowl waisting a first round pick on a toolsy QB who will never be more than average hurts in the short and long term. The first round guy usually starts in year 1 and more likely than not isn't great and doesn't go anywhere especially if there is a weak team around him. Then that guy shows flashes in the first couple years giving you hope for better things , but isn't elite, however in QB starved market you have to spend a huge portion of your cap to keep him there because supply fort even serviceable QBs is limited. All of this just to end up with more average performances. Guys like Tanehill, Cutler, Bradford exemplify thids and to some Stafford and Matt Ryan would be in that class without 2 of best receivers in our Generation Julio Jones and Megatron.
If the goal is the Super Bowl, you need a legitimate QB. "Wasting" a first round pick on a WR when you have a journeyman backup QB doesn't aid you in that goal.
P.S. Two of the QBs from the Super Bowl list above were toolsy QBs that played at small schools and were drafted in the mid-first round. Didn't pan out too poorly for the Ravens and the Steelers.