For a bit of perspective, here are McCoy's stats compared to the early-career numbers of a similarly-sized QB that did end up making it good:
|Yards per attempt||6.2||6.3|
Colt, though younger and with less time in the league (Sipe was a 1972 draftee), stacks up pretty well against a guy who later turned into the league's MVP and one of the top three quarterbacks in Browns history.
Both QBs played for subpar Browns squads and endured coaching changes during their early careers. The biggest difference is that Colt takes better care of the ball. When he can't find a receiver in time, he's more likely to tuck it in and gain what he can (or at least not lose as much in sack yardage).
Of course, the eras differ, with today's rules much more offense-friendly and protective of quarterbacks. Sipe won more games during this period, especially in 1976, the second year under head coach Forrest Gregg. The Browns actually had a 9-5 record despite being outscored by 20 points on the season. Sipe just had that intangible quality of, well, magic.
Colt could have it too. He's a tough, smart, charismatic leader. With more time, development, complementary players, and luck, he could become a stalwart behind center in Cleveland. It's just a bit too early to say.