Well, obviously it all comes down to numerical parameters in the end. But instead of having a set of generic ministers with 1-2 traits like +5% IC, I would like more personalized leaders. Obviously only a few dozen important figures, not hundreds of them.
Those famous ministers like Himmler should then be fully fleshed out and unique. Look at Himmler in "Darkest Hour":
That's thus far the best implementation of ministers we had in HoI games. In the end it's only more modifiers than in vanilla though.
So I'd go for more personal traits like loyal, zealous, timid, reckless, sick (like FDR, give him a monthly chance to die due to his illness) etc.
Traits that make the person come alive, like the CK-characters.