Alex Mack is one of the great free agent success stories in Falcons history, full stop. Few free agents have been better or more impactful than the potential future Hall of Famer, with only Michael Turner, Terance Mathis, and John Abraham (I know, technically) coming to mind as other recent examples.
Through his first three seasons in Atlanta, Mack has either been the best or one of the three or so best centers in the NFL. That kind of stability and quality has made up for holes elsewhere on the offensive line and enabled this team to field a Super Bowl-caliber offense in 2016, as well as very good ones in 2017 and 2018.