In AoE II, buildings castles was a pretty safe way of securing a location. Raiding under an enemy castle was suicidal, whatever you wanted to accomplish below it was more than likely not worth the expense of fighting under it. You basically had to leave that zone be until you had trebuchets or bombards in Age IV. Or if you were ballsy, you could attempt a ram rush earlier than that.
In AoE IV, trebuchets can be built in age III. So right away, keeps are weaker, because their hard counter can be produced earlier. But that’s not all.
I’ve also seen armored units successfully harass my economy while under keep fire and losing like 3-4 units max doing it. I’ve also seen them taking down the keep itself without too much trouble.
Now, you can upgrade your keep by making it sturdier and deadlier. That’s great and all, but investing this many ressources into something that can just be taken out for free at a distance by trebs or bombards feels a bit wasteful.
The thing is, if this was like AoE II where castles could also train units and research some technologies, it wouldn’t be as bad. But in this game, keeps are nothing but big towers, and yet they’re weaker than the multi function castles in AoE II. On top of that, they’re also more expensive. 800 stone instead of 650.
I’m sure some people like keeps being weaker, as one could argue it makes games faster paced. But personally, I liked placing down a huge building and knowing that that area of the map was secure