But then you have a class like the bounty hunter where three of its five companions use aim and the smuggler where two of five use cunning.
I agree that "ninja looting" is a problem but your solution is a non-starter.
Actually to be able only to need on items your character can use and benefit from and remove the need button from all other classes is a good start.
It will remove the random need spree that is currently in the works of many players. If your character can equip and benefit from the stat it will never be ninjalooting. To take a item that you can use and decide not to use yourself is more about bad judgement then ninjalooting.
Changing the lootrules to common sense is something many other MMOs has done with great success. It simply removes the many problems and frustrations that occur with players taking stuff they can not use.