I had the following position with black in a game I recently played:
[FEN "r1bqkbnr/pp1n1ppp/2p1p3/2Pp4/3P4/4PN2/PP3PPP/RNBQKB1R b KQkq - 9 5"]
and proceeded with 5... e5
However, after the game was over, while reviewing it with a chess engine, Stockfish suggested 5... b6 instead and gives -0.16 (equal)
I find this very confusing. I was taught in Nimzowitsch's My System (among in other sources) that one must undermine a pawn chain at it's root, hence e5 seems appropriate.
So my question is: without looking deep into variations, why is in this case b6 a good move (in principle)? Wouldn't white follow up with b4 and have a nice position?