I've heard people complain about being betrayed immediately and not being able to trust anyone for even one second. The specific post I mention wanted a cooldown for breaking alliances, but I personally disagree with that.
I think it might be better if the debuff is dependent on how long you've been allied, meaning that the debuff is greater just after an alliance. An example might be: for the first 5 minutes, a 35% debuff to defense. After that it becomes 25% or even lower. This means that betrayals cannot be made on a whim, but they can still be a viable strategy in the game. My only worry is that it might make long lasting alliances less likely.
All this being said, I also don't mind it being the way it is now, just another idea that might be interesting to consider. I'd genuinely be happy to hear why this might be a good or bad idea, or other feedback