The day of the first Dooms Day patch had the mechanics broken, my archers were running foward and dying in Valleys becuase they got infront of my warrior meatsheild. I also was wiping 1k ballista on lvl 5's becuase they were suicide running. I think that this was the cause of the second patch that day, and the source of the myth. lvl 8 HBR is the magic number for 0 losses vs a lvl 5 npc, Any less and you will suffer losses, not 100% sure as to why.