My default formation is one of the hardest counter against 41212. It is asymmetric, though.

The hardest counter against sole defender flanks (DL DR and no other flank) is 3 players on the flanks (two on one side and one on the other), and the two-player flank being AMR+DMR (or AML+DML). My default formation meet these requirements.

451V is popular a counter against 41212, but not effective enough to be called a hard counter.