Two issues, which seem to have been around for awhile.
Firstly, can AI's be encouraged to update their special units, & not let them stay around for ever. In current game Persia had an army of immortals which sounds good, & had biggest army. America declares war & pummels the Persians, who seemed to have no range units at all & comprised nearly of Immortals. Now this would have great in classical age, but America like most civs was reaching the Rennaisance, & its modern army took them down. Even when they were destroyed they kept building more, probably due to low cost.
Secondly, & a bug bear to myself as well as the AI, is when new units come onboard, whether built, bought, or gained my other means, can they not just be put out into that cities tiles. Particularly, when at war, & a useful unit suddenly gets put on the front line & destroyed that turn. Poor Persia actually obtained two Longswordsman who were put right next to America's finest & obliterated. Is there any way when a new unit comes onboard that the player/AI can actually move it to a tile within city.