Agree to disagree on that part. There's a huge drop off, not only from 1-20 but from the #1 overall QB prospect in a given year and then another year. For example, I bet the Bears wouldn't have taken two 1st round picks for Caleb Williams, even to go from #1 to #2. But they did that exact same thing after doing some diligence on Bryce Young. Similar story with Trevor Lawrence and Andrew Luck: they were simply not obtainable. But Jared Goff and Carson Wentz were.
There are often still good QBs as late as around #10. But you get to the 20s and it's a huge difference. Especially when it's the first QB taken. And yeah you listed a lot of hits that went 15 or later but how about the misses from 15-64? Will Levis, Mac Jones, Dwayne Haskins, Drew Lock, DeShone Kizer, Paxton Lynch, Christian Hackenberg, Teddy Bridgewater, Derek Carr, Jimmy G, EJ Manuel, Geno Smith, Brandon Weeden, Brock Osweiler, Andy Dalton, Tebow, and Jimmy Clausen. That's 1-2 franchise guys (Dalton and maybe counting Carr), 1 maybe good (Geno Smith took him 9 years and jury is still kind of out), 1 dude who got to play in an elite scheme and sucked otherwise (Jimmy G), 1 serviceable backup/Pickett level guy (Teddy B), and the rest are busts. It's mostly a dead zone over the last 15 years. The guys you highlighted are huge exceptions and some of them are 20 years old at this point.