Went through 3.5 and 3.6. I just noticed that Owen’s defense, Nimzo-Indian and French defense have very common ideas: white has pawns in d4 and e4, and knight on c3, while black has pawns in e6 and d5 and bishop on b4 pinning the knight. So I guess the same principle applies to all of them: c-pawns are important to open things up, black needs to break things through by c5 or f6, white can play Nd2 instead of Nc3 to avoid …Bb4, etc.

P.S. now I think more about it I feel French defense is more akin to a queen’s pawn opening rather than a king’s pawn opening because of the d4-d5 structure.