Football is an entirely different game when the defense can actually hit you. We have no idea what Zach Wilson is capable of and people are already calling for him based off of practices where they're basically out there playing catch.
Tanner played poorly the last 2 years, but he was in an AWFUL (can't stress that enough) offensive scheme. So throw those two years out the window. Mangum played decent as a FRESHMAN when he was in a different offensive scheme. And that was fresh off his mission. Now he's a senior, he's playing under a new offensive system that presumably will play to his strengths (honestly anything will be better than the last 2 years scheme). To throw him out at this point is absurd.