I think that anywhere in the Uni where there is a defense upgrade cost reduction, it should be changed to upgrade time reduction.

For example, under Leonardo, it should be 10 researches for upgrade time on mortar towers, not upgrade cost. This will reward everyone who has taken or will take the time to work Uni research to get a small reduction of upgrade times.

you have towers under Sejong, mortars under Leonardo, Tank Depots under Saladin, Anti-tank guns under Sulemain... it only rewards those that research it vs the previous recommendations of applying it as a blanket percentage for all lower ages.

all of the researches could be capped at 10% reduction too. It would only take a little over 1 day off for most upgrades AA and beyond, but it would help players