I think the biggest balance issue should be that many civilized castle soldiers have been almost replaced by conventional troops

The infantry ethnic group is the most severe in Japan, Aztecs, Vikings, Darovita, Celts, Teutons, and Inca. The unique units of these ethnic groups are distinguished by being stronger in hand to hand combat than the champion swordsman, with most moving faster than the champion swordsman but having lower basic shield defense (AZ has just been strengthened with 2 shields, while Teutons have more health and 2 shields, but cannot catch up with the archer)
I think a very useless feature unit: Malian Swordsmen (Malian has a complete and bonus cavalry route, which has low health and defense, and is even less reliable than muskets. In the castle era, the harassment effect was replaced by cavalry, and in the imperial era, the rear output was not as reliable as muskets)
Burgundy’s light cavalry (this unit was originally a nemesis against low health units and requires pulling operations. The main reason for weakening is due to multiple weakens rather than the design itself)
The Centurion of Rome (this unit is purely a tool unit that provides an aura for swordsmen, but its elite upgrades are very expensive. Although it can earn bonuses by upgrading its elite, I still feel that its attributes are not much different from those of the ranger, and its design is very mediocre. Moreover, when Rome needs cavalry, there are also heavy knights with technology and bonuses that can be used)
I think the least useful unique unit is the British Longbow (compared to the Crossbow, the Elite version has an additional 1 range, 1 attack, and 1 shield defense, with a gold cost of 5 and a wood cost of 5, but the unit’s lifting action is much slower than the Crossbow, and its hit rate is also 10% lower than the Crossbow. This results in its range advantage sometimes even having no effect, whether it is shooting charging cavalry or stationary units, it is easy to miss, and the hit and run feel is also very poor.
It is worth mentioning that many characteristic soldiers of civilizations are designed reasonably, with neither low nor high intensity, to compensate for a disadvantage or disadvantage of their own tribe. For example, the cavalry route of Malay cavalry is very poor, so they have obtained fast infantry but can only harass or attack siege weapons. Komen did not have a third level range, so he was awarded the Qincha Shooter.
Some people think that powerful specialty units are not as powerful as they imagine, such as Frank’s Axemen, who is usually considered an excellent combination of auxiliary cavalry. In fact, on the Arab 1v1 map, unless there is a huge advantage, you cannot upgrade the technology of both Axemen and Ranger to achieve this combination at the same time. This is a huge test for Gold. If you need to help Ranger clear the Long Spear, it is better to choose a fire gun that is easy to form and efficient