49ers QB Alex Smith may not be an elite quarterback, but he's doing essential quarterback things like calling the proper audibles in the running game, converting third downs, and avoiding mistakes.
A key reason for this is that HC Jim Harbaugh has made the passing game easier for Smith, particularly when it comes to beating the blitz. Of course, coaches often say they are "simplifying the playbook," but Harbaugh has been able to do it coherently and in a way that actually aids his quarterback's ability to succeed rather than simply removes options.
Harbaugh has changed the entire theory behind how Smith and his offense approach the blitz, and this is where Smith's greatest improvement has come. That's because Harbaugh eliminated "sight adjustments" from the 49ers playbook.
A "sight adjustment" by a receiver refers to the concept that, if a defense blitzes, the quarterback and receiver must both — on the fly and after the snap — recognize it and adjust routes accordingly.
So the 49ers ditched sight adjustments. But they still need an answer for the blitz, right? Harbaugh has one. If you want your team to throw the ball downfield, you must keep extra players (two running backs, a running back and a tight end, etc.) in pass protection to buy time for your receivers to get open.
As defenses get more complex, the answer isn't always to get more complex on offense; sometimes, it's the opposite.