The game is dramatically different in the NFL compared to college.
Yes Zach has a great arm. His NFL pro day is the type of environment where he's godlike in his abilities. He can make any throw.
In game is very very different. We've seen him play 40+ games in the NFL. We know who he is. He can be a solid game manager, which a lot of teams in the NFL need. Right now he's struggling to be consistent enough to be a reliable game manager (there's a reason he's QB3 and was a fringe roster guy). Upside is that he can be a starter for a team somewhere (that would be a dramatic rise for a QB3) and he a reliable game manager.