Couch was good, and hamstrung by the following:
1. Mumme's system didn't just not prepare him for the NFL, it didn't even try. There were reports that Couch had never been taught to read a defense properly. Mumme's system was spray and pray, essentially.
2. If you think Cleveland was a mess now, they were even more of a mess then. Had to build from nothing as an expansion team, insane front office, incompetent old school coach, probably the worst o-line in the modern era, one competent WR, no RBs, horrible defense. He was David Carr before David Carr.
3. Every other first round pick in his era failed to do much
4. Tore his shoulder up and never recovered.
Interstingly, he's still the Browns all time leader in completion percentage... at 59%. That should tell you all you need to know about Cleveland. (took that from wikipedia, appears to be wrong, but there may be some sort of games played cutoff)