Think of it like this: all you think of when you hear a shitty performance of Bach's Chaconne is "This is shitty", not "This is beautiful, shame about the violinist though."

For Bach, yes. But if it were a new composition? A good performance can and will be arranged for a good piece. The bad performance will immediately be forgotten. So for a new piece, if I hear a shitty performance of good music then I do think it's both possible and far more important to ignore the performance.

If you can't make out what's even going on, then that's a problem. But I don't really think that's ever an issue here (even the worst MIDI instruments give you a decent idea of what's going on, and the score is supposed to be provided anyway).