Rodney Peete was a sixth round pick, Barkley fourth, Booty in the fifth, Rob Johnson fourth... Leinart, Sanchez and Marinovich weren't good pros, but 1-for-4 is a lot different than 1-for-8, and it's probably more that the sample size of highly regarded USC quarterbacks is too small, and spans too many years, to make any conclusions anyway. (In fact, if you're trying to determine "what leads to QB success in the NFL?", the pedigree of the college program is probably like 50th on the list. Mahomes went to Oklahoma, but Aaron Rodgers went to football powerhouse California, Lamar Jackson went to Louisville... Drew Brees went to Purdue, which is a power conference school but not a national title contender.)