Considering that some of them would be OP if uu are too easy to produce, I try to give some rebalancing as a reference:
Camel archers 50w 60g→70w 60g(in military buildings)/training time: 25s(before conscription)→37s(military buildings)
Arambai 75w 60g→100w 60g/21s→33s
Kipchak 60w 35g→80w 35g/20s→27s
Elephant archer 100f 70g→135f 70g/25s→39s
War wagon 92w 60g→120w 60g/21s→33s
Plumed archer 39w 39g→54w 39g/16s→27s
Mangudai 55w 65g→80w 65g/26s→39s
Conquistador 60f 70g→85f 70g/24s→38s
Magyar huszar 80f→95f/16s→18s
War elephant 170f 85g→220f 85g/25s→42s
In addition, huns, Poles, goth and sicilians always keep their silver crown only in castle.
I am tired of explaining.
only when you lost all castles and run out of stone,
when you have castles around your backward base but need to fight at forward base,
when you need uu to counter enemy’s army but have no more time to build castles,
you will realize that castles should not be the only place to create uu.
AND nothing will be changed in most of the other situations.
unfortunately, you will regard the buff for infantry uu as OP’s suggestion too before you know it is confirmed by official, because you are afraid of any big change.
things like OP and rebalance are just your excuses，the fact is that some old player like you just want to keep the original state ，in case they can’t adapt to the new situation.
It’s not lacking a castle that prevents The castle age UT are still rarely research in castle age the there are some exception that would be op like the poles. but for 90% of civs Committing to a castle age Ut is committing to a slower imperial age which is not worth it.
actually imp age ut is always researched before castle age ut, but things can be different if ut moves to university.