I don't mind a few commander being kept as rewards for play, so long as that number remains small. It offers dedicated players some rewards, just like the way that unlocking based on level did.
Now, there is a problem that, at release, 50% of the OKW/US commanders are only obtainable this way.
Hopefully, as more none-drop and buyable/earnable commanders arrive, the problem should go away. As it stands, it's a little suspect.
The russian commanders are already large in number, so having some rare and obtainable ones is great, IMO. Still keeping fingers crossed for No retreat No surrender