In a recent Pantheon game I wound up fighting a zero opponent fight against just the static defences + reinforcements. (reported elsewhere)
I took the enemy portal and cleaned out all the towers, but I wound up taking quite a while to kill the enemy Citadel, as it appears to deal massive retalliation damage each time it's hit. My (unupgraded, save new types) reinforcements that attacked the citadel each died in 2 attacks on their part. When attacking it myself it turned out I took 500 damage on each normal attack. (not when using spells though)
Is this as intended?