This picture of a Joseon period Korean flail cavalry could give you some idea about its reach. Flail cavalry shouldn’t be a UU since it was used by many North Asian peoples like the Tanguts, Khitans, Mongols, Jurchens/Manchus, Northern Chinese, and Koreans. In fact both the flail cavalry and the firelancer could serve as potential regional units for East Asian civilizations.
Your proposal of the firelance as a unique tech for pikeman is certainly interesting and it offers new dimensions to the use of pikeman.
Alternatively, the firelance could be a regional unit shared by Jurchens and Chinese (possibly Koreans as well), and it’s basically a flamethrower similar to the fireship, can be considered as its counterpart on land, and deals bonus damage against siege and buildings.
We have a lot of melee cavalry UU as well, such as Tarkan, Boyar, War Elephant, Leitis, Konnik, Coustillier, Keshik, etc. It would be hard to make the Iron Pagoda distinct.
I have never stated that the flail is the own weapon of the Jurchens.
There are camel archers for Berbers, axe throwers for Franks, plumed archers for Mayans, which mean the UU is not necessary to be unique in the real world. The point is they used them well or not, and Jurchens surely used flails and even introducing them to a Manchu empire in AoE3. Introducing them as UU is making sense and interesting.
The problem of the fire lances is that they are too much impressive as weapons invented by the Chinese. It is similar to give the Persians the Indian melee elephants that the Indian civ doesn’t have. So the better way of them is be a regional unit or an editor unit. That is different from the flail cavalry in some degree.
This would be a very bad idea either its useless or op depending on how you use it and its too much micro.
Most of the uu’s are cavalry as only the rich could afford horses. unless its a meso or a militia army based civi its perfectly fine to have a cavalry uu.
pretty much all weapons are like this name one civi in the world that did not use bows axes spears or swords.