Joe Alt's presence on the Chargers' offensive line was one of the key driving forces to their wins this season. Before even getting into any fancy advanced metrics, just look at their record. The Chargers are 4-0 when Alt starts and finishes a game. In the games he didn't play or left early due to injury, they're 3-4.
The Chargers have had over 20 different offensive line combinations as a result of the injuries to Alt, Rashawn Slater, Trey Pipkins, Mekhi Becton, and others. Prior to the Chargers' loss in Jacksonville, OC Greg Roman talked openly about the lack of continuity along the offensive line being a problem.