A QB that can make the progression of reads quicker and is mobile would do much better than Drew. Drew needs 5 seconds at least to make his progressions. We all know he isn't going to get 5 seconds unless he can scramble around.
A mobile QB can buy more time until he can scan the field or a WR come back and gets open. This translates to more 1st downs and point.
We know JP Losman is more mobile, we are yet to see if he can make the reads. As far as Mathews, can he be any worse? We are losing now so what difference would it really make?