Hello Robert,
I can't say that I complicitly agree with you're suggestion.
I agree with you on the basis of real world practice, but as we see with everything in WHF & 40K; not everything is relative.
Also, when it comes to knights, as everyone knows Bretonnians are the Orc's nuts!
Other knights are "average". Imperial Knights of the Order get the highest cavalry armour save and Chaos Knights are tough and nasty.
I do advocate for order-specific magic banners.
So, for eg; the Reiksguard are immune to Psychology, Knights Panther get +1 Initiative, Knights of the White Wolf cause +1 damage on the turn they charge with their cavalry hammers (for a total of +3!), Knights of the Blazing Sun recieve a +5 ward save on the turn they charge. Of course, you can add more than this to represent other orders...