You don't NEED one, that's true.
But getting a franchise QB, you're dependent on supply. You figure only one of those guys come out every year, maybe two, maybe none.
For as banner a year as 2012 was supposed to be, the 'correct' choices were only Andrew Luck and Russell Wilson. The former went #1 overall and the latter virtually nobody saw coming (no matter how much they try and pretend they did, after the fact).
And 2011 was one of those years where a bunch of unique QBs came out, but again the only 'correct' answer was Cam Newton, who went #1.
Honestly that's probably going to end up true about 2019 as well, with the only 'correct' answer being Kyler Murray, unless there's a lottery ticket hidden somewhere.
I remember last year 2018 was supposed to be another glut year, similar to 2012. Yet what if the only 'correct' answer turns out to be Baker Mayfield, who went #1 overall?
And back in 2016, when there were arguably two correct answers although many will still express discomfort with either Jared Goff or Carson Wentz, you had to be picking #1 overall or #2 overall to get them.
From where I'm standing it looks like the NFL may actually be getting better at figuring out which guy belongs at the top...and the rest of the NFL are left picking and praying.