I get what you're saying. I'm using the fish as an example of a greater (and more prolonged) stressor than the cast. I've never had a break during the cast, either, now that I think about it.
My thought is that, as long as the leading edge of the knot (which is what I assume would see the greatest amount of force should it strike a guide ring during a cast) is braid, then the braid side of the knot kind of cushions the weaker line.
I don't mean to sound like I'm trying to convince anybody to abandon their knot. I understand that's a deeply personal thing.