I see traits as additional training. It should take extra training to function efficiently in armor. Even at 81% armor, you only get -4 Init. So you can trade 4 Init for Bloodthirsty or Charge. The question is how you want to focus the unit. The best thing is that as the game progresses, there are more and more factors that affect whether or not you should take Muscle and Strength or perhaps just Muscle if you can get away with it. Full Plate should require a horse, Muscle, Strength, and some light magic to have no Initiative penalty if we are looking for a good balance.
Of course this is where I would point out that each piece of Plate give a penalty of -1 and does not weigh much more than chain. This is where I start changing things and the conversation gets convoluted.
