Is this a bug or is this much stacking working as intended with sub city generals? -80% ground defense from one Cixi and 3 Wallace seems like a bug that can be exploited and could create frustratingly unbalanced gameplay.

I understand Cixi and one Wallace debuff stacking for -40% ground defense. But, the additional -40% from the 2 other Wallace seems like a bug since this is not how rallies work.
If this is not a bug for sub cities, then gameplay will become very frustrating when people start attacking and defending with 8+ Nero’s and -80%+ HP.

If this sub city debuff stacking is intended to work like this, please confirm so my team and I can start filling out subs up with our super debuffs of choice.