Lesson 1: When you can't stop the run playing defense gets hard. The signs of rush defense being a problem were evident in the preseason. Defensive lineman that struggled both to get push and get off blocks. Cody is worthless. Out of shape and can't play low enough to get leverage. Add in poor tackling and you get one of the worst rush defenses in the league.
Lesson 2: Flacco isn't good enough to carry the team. He is not a elite QB, simply a complementary player. When asked to do too much like the last few weeks he makes mistakes in ball security and lacks accuracy in most circumstances. Flacco is better than a lot of QBs in the league but he needs the elite defense that the Ravens have historically had.
They will make the playoffs but it will likely be a one off situation. The injuries have hurt the defense greatly but the rush defense issues preceded that. Lot of soul searching to done in the offseason because the window has closed on the current configuration and it is likely time to say goodbye to Lewis, Reed, Boldin, Keomatu, Cody, McKinnie, Williams, etc.