He didn't look "terrible" in his time in the NFL. He won two games on a terrible Browns squad

Two wins against equally terrible teams (3-13 Titans and 5-11 49ers) isn't really evidence that he wasn't a terrible QB. He did not look like a good player on a bad team. He looked like a bad player on a bad team. The Browns were bad in 2015, and he was a big part of that. There really isn't any way to spin a 57% completion percentage and more turnovers than touchdowns.

it's just not as stupid as everyone wants to pretend it is.

Nobody is "pretending" anything. It would be a stupid move for any team, much less the Falcons who have concerns about making it back to the postseason in an ultra competitive division...not embarking on a reclamation project in hopes that he'll turn into a backup QB.