The only problem I see with changing weights is the window of success . I think the game engine is modeled to use the full scope ratings across all positions . Tightening up certain parts have certainly made them touchy. The success / failure rates are working in smaller windows . I don't know why that is bad but it certainly doesn't feel right In a general sense of balance or available ratings .
Custom leagues should be able to choose to change the default weights as well. Logic has me thinking it should effect the trade meter too!