Okay fine, it's technically possible to defeat a player defending by himself with 9 cities if your alliance has 100 players all with lvl 10 archery, and is willing to sacrifice somewhere in the range of 15-20 million archers.

which would mean 150-200k archers per player to kill a single player by himself, no alliance reinforcements. Or, more or less the entire armed forces of an alliance of advanced players. post-refuge.