I somewhat agree, I think the talent level is better, but not necessarily better or as you put it "exponentially" better at finding a good QB vs the lower rounds.
Even the example you used is a 5% increase from first round to later rounds.
Frankly there are far more busts in the first round of the NFL draft at QB then later rounds, which I believe is mostly due to over reaching at that position since everyone is desperate to find their next guy.