There is a gap, but it's not like the rest of the AFC has terrible QBs and only the Bengals and Chiefs have anyone who's any good. You are making it sound like it's Burrow and Mahomes and everyone else sucks. Trevor Lawrence was so much better this season than he was last season, when he was coached by Urban Meyer. He can only get better. Herbert is a really good QB, it's been the coaching that has been the problem. Allen has been better than all of the other Bills QBs that came after Jim Kelly (except maybe Doug Flutie) and before him. He's 1000 times better than JP Losman, an aging Drew Bledsoe on the tail end of his career, Trent Edwards, Ryan Fitzpatrick, Kyle Orton, Tyrod Taylor and EJ Manuel. The Bills even had Thad Lewis and Jeff Tuel start.
Are Mahomes and Burrow the top two QB's in the AFC? Yes they are, but it's not like the other 14 QBs are mediocre. Lawrence, Herbert, Allen, Tua (when healthy), Jackson (when healthy) are all pretty good. The jury is still out on Kenny Pickett. Ryan Tannehill is the AFC version of Kirk Cousins. Everyone wants the Deshaun Watson experiment to fail in Cleveland. Mac Jones was coached by Matt Patricia and Joe Judge.