'twas a fundamentally different era. Especially in the AFL, which Namath played in from 1965-69, it was not uncommon for quarterbacks to complete fewer than 50% of their passes. Namath once responded to that criticism by saying "Sure, I could complete 60% of my passes if all I did was dump it off to my tight ends and running backs." That was the era of the "Mad Bomber," so to speak.
A case in point was the "Heidi Game," vs. the Raiders in 1968. In the fourth quarter of that game, "New York defensive end Gerry Philbin recovered the football at the Jets' 3-yard line setting up a 97-yard drive, consisting entirely of two Namath passes to Don Maynard, who was covered by Raiders' rookie cornerback George Atkinson. The 50-yard touchdown pass followed a 47-yard throw, and gave the Jets a 2622 lead" (https://en.wikipedia.org/wiki/Heidi_Game). And, yes, both of those passes were bombs, not short or intermediate routes with significant yards after the catch.
Namath was the first pro quarterback to throw for 4,000 yards in a single season and he did so in 14 games (1967). During his career, few quarterbacks put up the overwhelmingly positive TD pass/interception ratio seen today. For comparative purposes, consider the following stats for leading QBs of that period:
Johnny Unitas: 290 td passes, 253 ints.
Bart Starr: 152 td passes, 138 ints.
Fran Tarkenton: 342 td passes, 266 ints.
Lenny Dawson: 239 td passes, 183 ints.
Daryle Lamonica: 164 td passes, 138 ints.
In short, it really isn't fair to critique players of the past based on contemporary statistical standards. However, since you specifically asked about Namath's performance in college, he was selected first overall in the AFL draft after finishing a three-year career at Alabama in which he completed 203-374 (54.3 %) for 2713 yards, 25 touchdowns and 19 interceptions.
I watched Namath in college and in the pros and Stabler was a better QB on both fronts. But you can say what you want about both of them but neither of them would compare to Peyton Manning. In fact, I would say that Casey Clausen was better than both of those guys.