Why would I want a Central Defender with 20 speed and 21 strength? Or 18 shooting just to finally get 17 passing?
We would get a better market and more unique team compositions if we could train specific skills.
If you think that DC doesn't need speed and strength then you're just dumb... And to improve let's say passing just add to attacking skills see if it adds to passing if not simply don't save it and add to defense instead, the next day it may add to passing.