I completely disagree. UUs obsolete, but UIs are given in the same slot as a UB, and UBs are definitionally better than the base building they replace. If nothing else, all UBs give at least some base yields over their base building. If UIs obsolete via being made worse than a base improvement, then that civ is worse off than any civ with a UB, because they are functionally playing with no unique infrastructure bonus once the base tile improvements overtake their unique component to put it another way, you are arguing that a civ with a weaker UI will simply have to have a strong enough UA to carry them through the late game, after all their other unit and improvement bonuses are cast aside. They will have to still go toe to toe with civs whose unique market or aqueduct will never revert to a lesser version of itself, after all.