One new building requiring a complete redesign of army construction from the previous 6 ages, and becoming the central focus of all attacks where it is present is ludicrous. If it stays in the game, it needs to be made it into a real, balanced building appropriate for regular pvp as well as war.
To do that almost certainly requires some combination of:
Limited range - there should be a significant drop zone that it just can't see, and won't active until the appropriate HP are inside the range.
No or very limited splash damage - only hits the top 2-3 highest HP units in range.
Limited damage - low enough to not instakill a howitzer. Maybe scaled to unit - 2000 damage max, but can take no more than 50% of an individual unit's HP in one shot.
Reduced firing frequency
Reloading cost.
I don't know what the best combination of those is, but I see this as a game breaking building. For a mobile game where your ability to continue playing is limited by your ability to keep troops and planes alive and not use too many tactics, a building with this level of unstoppable troop killing capability makes no sense.
If the designers want to keep it, rescale all training times so I can rebuild my entire army (including generals, planes, tactics and all troops) for a reasonable price in less than 15 minutes, and 5 on a training blessing. Then I can attack and deal with the probable loss of all troops and use of all tactics, and continue playing the game without taking a minimum 2 hour break for planes.