To jump into the arm strength conversation, the thing is that Brady's arm strength didn't become very good until 2004'ish, IMO. If you watch him throwing the ball in 2001/2002 compared to 2004 onward, there was a clear difference. It appeared to be both mechanical and physical; he clearly improved his frame and added physical strength, which no doubt helped his arm strength. He also appeared to tweak his mechanics, elevate the ball a bit higher, get more leverage with his elbow/shoulder, have a slightly nose-down trajectory when he released the ball (this latter point is also a massive reason why Brady is such a successful QB in adverse elements; throwing a slightly nose-down ball in windy/wet/cold conditions is a positive thing).
I think Mac's arm strength coming into the NFL was similar to Brady's, maybe slightly worse. I fully expect his arm strength will improve, both physically and mechanically. I expect Mac's arm will be noticeably better this season (although it may taper off after 75-80% of the games just due to attrition and him still being a 2nd-year player). By year 3-4, I think Mac's arm strength will be more than adequate and will no longer be a relevant talking point (similar to Brady at that juncture in his career).
