[commissarwhiffy]

I play a wholely Cadian army (they look cool) as well as if you play a specific army, you'll often get more than the base 5 doctrines (see errata). Personally I Always use Iron discipline on my officers, and usually sharpshooters on my support squads. I find that BS4 in a basic squad doesnt usually make a huge difference.
I would have to vote for the 3rd option, they should be army oriented but its just not points practical to do it.