Just a suggestion, but wouldn’t it be possible to make the Champion and its group invulnerable if one of the keep’s/tower’s walls/gates are not down? For instance, in a keep, if the external wall and door are completely intact, and the internal wall/door are completely intact, is it possible to make the Champion Defender and its group invulnerable? In this way, it would be necessitated to have breaches, and keep defense would play its intended role.