Knights having bigger rank bonuses is a bit silly, since they already get higher unit strength to represent their steed combined with them.
I don't think our knights need any tweaking at the moment; we've already got them as a core choice, relatively inexpensive, AND the option to bring magic banners into battle with them (I'm considering taking the Daemonslayer banner against horde opponents where leadership is wanting). There's not much need to improve them, and taking a mounted WP makes for plenty of attacks.
Honestly, I'm pretty happy with empire overall, to be honest. I think we're definately one of the most balanced armies out there. I'd like to see a little tweaking on engineers to make them a seriously viable option, and maybe mortars as indirect fire. Beyond that, not many complaints rules wise.