A great filter is a weak explanation for the silence, because it would have to work every single time — one civilization with self-replicating probes could fill the galaxy.

That is absolutely possible. I’m actually putting less credence on that one just because you need to happen every single time. If even one, I mean, this goes back to John von Neumann pointed out that you don’t need to send the aliens around the galaxy. You can build self-reproducing probes and send them around the galaxy.