Before you cry heresy, grab your warhammers and smite me with holy fire, this post is not a subjective, "oh I like Cathay's design more, blah, blah, Empire sukz."
No, this is merely an observation having played both Cathay LL's and both Franz and Gelt for 50 turns at least.
Nearly everything about Cathay is simply better. Cathayan units are statistically superior, and with Harmony, often by a significant margin, they are easier to access in many cases as well, requiring lower tier buildings and few if any cross building combinations, in fact, I don't think Cathay has any "x building unlocks x unit but only if you have x other building already built."
As a simple example, a tier one barracks for Cathay gives access to Jade Warriors, who start with either 80 armor or 95 armor depending on which LL you play. That increases by up to +20 armor if they stand still for long enough. Back them up with a few peasant archers, who outrange empire archers, and Jade Warriors have nearly identical MA and MD as empire swordsman. Sure Jade Warriors are more expensive, but they are SIGNIFICANTLY better as a front line unit than empire swordsman who a whopping 30 armor or 40 if you play as Gelt, who do not benefit from proximity to ranged units, and do not have any sort of passive bonus.
Cathay's low to mid tier units are simply better, and easier to access across the board than the Empire's similar troops, and they have greater staying power. On top of this, the Cathay Fire Rocket is so insanely strong as to be near mandatory in armies. And all of this comes while being richer, safer, and easier to play in general.
My point in bringing this up is that I believe Empire is in need of some serious quality of life improvements. Across the board Empire troops need a balance pass. More armor, higher leadership etc. General's skills need to be updated, magic needs to be easier to access, because Cathay has both easier access and stronger spellcasters.
Ironhail gunners are a tier 2 unit, handgunners are tier 3 and while they don't fulfill the same role, handgunners should arguably be tier 2 and ironhail gunners 3 based on their role and general utility.
There's more that could be done I'm sure, I simply wanted to share my thoughts, because while I really like Cathay, I really love the faith, steel and gunpowder of the Empire, the Men of the Empire need some help right now.