Currently daggers spawn based on the level of the city minus one (x-1, x being the city level). This allows them to be much more dangerous for sieging a capital or any high level city. Additionally, they will reduce the spt of the city to 0 for the turn. As a result, their costs has also been adjusted so they now cost 8 stars.
This is it. We *want* you to use them on high-level cities, and OP's suggestion does the opposite of that.