They are developed for open-field battle against Dothraki. Not as a police force. Dany has put her army outside of their element.
Yea, that's all fine and good, and I am sure that it lines up with the books, but considering the fact that those cats were castrated as children and dedicated their entire life to being elite warriors, I feel like they ought to be pretty damn deadly in any environment......they have just been a let down. If they ran across the Spartans, they would get their asses handed to them in a hurry.....and the Spartans still have their testicles.