In the Starting Line-Up
His arm strength is a concern. I hope he can improve this over time.
Can't say I agree. Mac's arm velocity isn't an elite strength (pun intended), but I don't think raw arm velocity is necessary (or even sufficient) for success at the quarterback position. Timing, decision-making, eye placement, preparation, pre-snap adjustments, accuracy, throwing players open ... those are the traits that consistently predict success of NFL quarterback's, not raw arm velocity.
Also worth noting that Mac is young and a rookie, which means two things: he has maturing to do in general (physically, mentally, emotionally), and he has a lot of headroom to grow into NFL shape since he has spent little time (relatively speaking) in an NFL facility.
He'll get stronger as he moves into his mid-to-late 20s and he'll get stronger as he trains within an NFL program specifically for the purpose of increasing core/lower body strength in order to improve arm velocity/zip.