Getting straight to the point, obsolete UTs can be removed, one UT can be given to a weak civilization, thus requiring less brainstorming to make new UTs, and contributing to the civ balance a little bit.
Weak ones can be dropped. Mild ones affecting UU can be incorporated directly in the stats. Mild ones affecting general units can be locked behind a tech. Strong ones can be traded for something in the tech tree.
Weak ones which can be dropped: Nomads, Stronghold, Orthodoxy, Madrasah
Corvinian Army can be dropped and Huszar cost can become 90F in total.
Mahouts can be incorporated in the stats of Elite War Elephant.
Yeomen can be traded for Thumb Ring.
Hill Forts can be dropped and Lithuanian TC Range can affected by Fletching line upgrades.
The real problem is when both the UTs are necessary for the identity of the civ like Aztecs and Bulgarians.
More Tech in the game give more strategical depth and diversity in the game. Why we have to go reverse way?
Argument like “UT useless in pro-play competitive scene should be drop” is pointless. Even researching nomad and delete house is fun when we play against AI.
Also, Town center affecting Blacksmith tech is tooo strong. Lithuanians TC will be invincible to Mangonel just after researching fletching which would become too OP bonus.
Some pro streamers try Lithuanians TC rush by researching Hill Fort to make fun of their viewers. Is it really harm for game?
I would rather think that introduce 3rd UT would be good to give more strategical depth in the game. Some UT would be useless, but some UT would be good to buff some underpowered civs. I like the fact that Forgotten introduce 2nd UT and African Kingdom introduce new University Tech Arrowslits. It is good to introduce new things in the game not remove it.
When would the tech become available though? In castle or imperial age? Would it be the same for all civilizations? Currently some of the balance comes from when the bonus is available to the civ in question more than that the bonus is available, if you made anarchy a civ bonus and perfusion a castle age technology the balance of goths would be changed considerably - on the other hand if Franks did not receive chivalry until the imperial age it would also change their balance considerably etc.
Honestly, if devs have no idea to introduce new bonus and UT, they should not introduce new civs to sell DLC. Introduce new ideas to the game is their jobs. Stole the bonus and tech in existing civs to make new Civs and make money? It is lame.
My point is, if we consider all parts of game including single play, none of the unique Tech is useless, and losing them will ruin some of their identity.
Civ buff/nerf should not be that way. Strengthen/weaken existing bonus or introduce new bonus is the way to change them like Tatars/Koreans new bonus introduced in November patch, not stole from other civs.
Also, the advantages of UT is that it is more easy to balance than passive bonus because players should pay for that. Imagine Hill fort is passive bonus even start from castle age. TC invincible to mangonel start from castle would be too much. How about Garland war? It would be too much if we give Aztecs passive bonus. But it is balanced for high cost.
UT is the good way to give some identity to the civs without game-breaking issue. We should introduce more UT to give diversity of the game. Should not go reverse way.