There's no doubt that having a mobile QB helps tremendously, however, that does not mean we had good offensive game plans going into our first 4 games with the QB's we had.
You don't HAVE to have a mobile QB to get creative on offense. You can still call misdirection, runs to the edges, counters, slants into the areas vacated by blitzing LBs, screens to RBs when the defense constantly blitzes you, etc, etc, etc.
Purdy will obviously help us to open some things up, but it certainly does not make any excuses whatsoever for the ultra plain vanilla offensive schemes we've had up until this point.