I think my reasoning was more along the lines of uniqueness.
Of course, for your KC-Bridge(Coppersmith) to work, you need some means to draw your deck, and for this, you need some other card. But there are plenty of them, be it Lab, City, Wharf, Councilroom, Smithy, Nobles, etc. pp., some of them with support from Villages or KCed-Cantrips, but as said, there are many of them and which one you take does not really matter. But cards which really give a high payoff in terms of coins are not so common.
My most loved KCed action in recent times was btw. the KCed Mint, which gained 3 HoP, which became Provinces the same turn...