Mike McCarthy has coached long enough to know where quarterback development usually starts.
The feet.
This is not just about throwing mechanics. It is about operating the West Coast offense. The ball has to come out on time, tied to the drop, tied to the concept, tied to the progression. If the feet are late, the read becomes late. If the base is unstable, the timing of the offense starts to erode.
That does not mean every quarterback has to throw the ball the same way. Different players have different bodies, releases, and natural movement patterns. But the lower half still has to operate inside a clear standard.
Drop speed sets rhythm. Foot placement directs force. Base integrity allows the throw to survive pressure. In a timing-based offense, the feet are not cosmetic. They are the clock.
The ball usually tells the truth about the feet first.