This brings up an interesting question, however... In the "real world" General Managers don't have "ratings" to put into a spreadsheet or equation to see how balanced a trade is. It's "gut feel" ... probably looking at the players history, talent, and recent stats. It does make you wonder if the AI shouldn't use the same logic - however (and this is a BIG however) if you go this route, you (as the REAL human) alos can't know the ratings, at least the detailed ones.
It might be interesting to think of this scenario... change what "we" see and what the AI "sees" so talent and recent history are the "prime" factors used in a trade scenario... would be more "true-to-life" and could result in some interesting trades......
ps: Brought this up only for discussion of an idea - not a recommendation that what's there is flawed