Based on my experience defending the city, I think a neat way to balance things out is to add a destructible door or pathway into the keep, but this location has loopholes (the
castle sort of loophole, not a glitchy exploit) that flank it on either side. This means that the attackers can try to infiltrate the keep through this second passageway, but a well prepared defending army could slow them down with a deadly crossfire if they're smart enough to hold that position. Consequentially, this would divert the bulk of the defending ranged players and give some more breathing room to the attacking force, wether they are actively assaulting the second passage or keeping the defending army occupied enough on that front with a few footmen to divert their attention.
Of course, this will probably never be implemented, but I thought it was a neat idea anyway.