I know nothing about DSL. But G.hn uses OFDM, and OFDM can do a cute trick in which it learns a complex number to multiply each subcarrier signal by. Since the subcarrier signals are literally just Fourier coefficients of the signal, this can equalize all kinds of linear time invariant signal issues so long as they’re reasonably compact in the time domain as compared to the guard interval. And I imagine that G.hn has some way to figure out which coefficients (subcarriers) are weak and avoid using or relying on them — there are multiple ways to do that.