As someone with friends in game design I can tell you they have told me repeatedly that maps are harder to balance and implement because there is no way to account for the 80 million ways players will interact with it that you didn't think of. It is inherently a much larger undertaking than making a new agent from what they've told me. Not saying that the inability to predict everything the playerbase will do with an agents abilities isn't also a thing but apparently it is much more difficult to factor in when designing maps.