CY is okay for balance. And speaking of big maps, it requires indeed a good amount of players to defend: If a good team of attackers make a nice move, they can destroy any defense (turret or tower), if they fail, that turret can be easily repaired so the team should prepare the aftermath from the other team soon.
Also I think as the CY is active, it should be able to self-repair as well. The repair rate on main buildings doesn't really matter for me, imo.