> 2. You hear the incomplete first measure as an anacrusis, or a kind of unaccented lead-in, to the second measure: OMG even more radical!

Why is this radical at all? This is exactly how most humans perceive it: as a lead-in to the second (I might even argue first) measure. It's very strange to me to say that most humans are supposed to understand the piece to have started before any sound is played. In fact that's quite preposterous: play a song that starts with a rest to 1000 people and ask them to gesture as soon as the song starts, and every single one of them will gesture on the first note played. How are they supposed to perceive the song to have started any earlier than that? A song "starting with rests" is written that way to make it understandable to the performer who is reading the notation. It's a purely notational thing. The notation is not the song, the sound is the song.