One of the complaints about the last CTS-V (at least in a Car and Driver comparo) was that it couldn't put all 640 horses down and thus got passed by heavier and less-powerful cars. It will be interesting to see if this car does a better job of it... but even still, without AWD Cadillac still isn't gonna catch ze Germans that it insists on chasing.
Conversely, Mustang isn't in a segment where AWD is prevalent, so no issues there.