It's a valid question, about how much arm strength you really NEED at the next level, for example in an Adam Gase offense.
Obviously Jay Fiedler was able to enjoy some amount of success with Miami, regardless of how much he's panned. I never worked up Chad Pennington because it was generally agreed he had a really weak arm so I didn't bother. He had off-and-on success at the NFL level. By the time Adam Gase had Peyton Manning, post-neck surgery, I'm not sure how much velocity you could count on from him.
I've done workups of Will Grier compared to three quarterbacks who are reputed to have 'weak' arm strength among NFL starters, those being Tom Brady, Drew Brees, and Teddy Bridgewater. I haven't quite gotten to DeShaun Watson yet, as that's the fourth one I commonly see cited by people on twitter who get all hurt when I start criticizing Will Grier.
I can tell you that versus the above three, Watson notwithstanding (we'll see), there's no comparison. All three have unqualified superior arm strength to Grier at all levels, every depth. And not insignificantly so. I think I've seen perhaps one or two Will Grier throws that have out-paced the very WEAKEST throws from one or two of the above players, on a similar distance...but only just so. The three produce much better velocity on a general basis, and when they really get all of a throw, their maximums are far and away better than anything I've seen Grier produce. Brady's maximums are at the ideal NFL starter level; Drew Anderson level.
Does that mean Will Grier is destined to fail as a pro? Probably. But you can't say that with certainty, obviously.
What would it look like for him to succeed? The thing you notice with the guys that have a little bit weaker arms is they're absolute EXPERTS in dropping the football into discrete zone vacancies between the numbers. It's touch and accuracy, but it's also an acute sense of timing, the ability to read a defense and instantly know what is going to pop open. You see enough of Tom Brady and Drew Brees not even bothering to use the arm strength they do have, because they're so good at this. Peyton Manning was an expert there, obviously.
Could I see Gardner Minshew getting there? Yeah. I could see that. He's a good thrower of the football, really good spin, good process, he's accurate, consistent. He's got that coaches mentality. Great character. It is really legit possible with him.
Do I see that being Will Grier's game? No. He's a gunslinger without a gun.