I have a bone to pick with UU that are otherwise well rounded but there one gimmick is they counter one unit type into oblivion units against some more rounded civs this isn’t a problem, but many of these units just invalidate other units that are essential to the strategies of other civs creating are civs wins. Many player would argue that you shouldn’t let player get to their UU which is good advice but misses the point. your gains opponent a substantial advantage because they got a castle up and didn’t not die, but what did they really to earn that advantage they didn’t really outplay their opponent but are rewarded regardless.
Camel Archers: counter cav archer if you play a civ like you Mongols, Huns, Tatars you are forced to basically ignored a large part of your identity or get punished.
Mangudai: your opponnent can no longer make seige the only exception being trebs and bombard cannons who can still be easily be sniped. You basically have no options counter play as Celts except hoang-rush and most player can’t execute a proper hoang-rush.
Genoese crossbow: Screw you Magyars, Mongols Berbers, Tatars, Cumans, franks and Huns,
Huskarl: Not only do i make archers irrelevant but i’m also created from the barracks the only way to counter me is HC and Melee units the later of which is counter by the rest of my Composition
Samurai: any melee UU
For the sake of comparison I think I should point out that that operate similarly but aren’t unfair to fight against
Rattan archer: High pierce armor but doesn’t shred your opponent’s archers can they still use their archers against your other units but still need an answer to your Rattan archers. Ex. Plume/eagle vs Champ/Rattans
Magyar Hussar: counters siege but unlike Mangudai they are a melee unit that can be deterred by halbs.
Plumed Archer: while powerful are not too big of a middle finger to infantry civs since they only deal 1/2 bonus damage are susceptible to regular archer counter and each infantry civ has a method of dealing with them (except Vikings). Goths have Huskarls, Celts have Siege, Japanese have FU Skirms, Slavs, Malians, and Bulgarians have good Cavalry.
Throwing axemen: are countered by archers and seige.