This is a slightly flawed list because the QB successes in particular are heavily weighted to the top 10 picks. Of the playoff QBs over the last 2 years, Mahomes, Allen, Burrow, Tua, Herbert, Goff, Stafford, Baker, Stroud were all top 10 picks.
When you’re drafting in the 20’s, you’re sifting through the Brandon Weedens and Johnny Manziels and Paxton Lynch’s and Patrick Ramsey’s and JP Losmans and Jason Campbells and Teddy Bridgewaters.
The only QB off the top of my head who was drafted after 20 in the first round and was a good player within his first few years was Lamar.