Is black plate worth it?

[Sombre]

In what sense do you get 1.4 smiths? That's a gross oversimplification. You haven't even shown that you get more gold or castles by building black plate over chainmail after the first couple of turns. You say you save gold, but you admit they aren't as good for quick expansion. I could argue that quick expansion nets more gold, which means more castles and smiths, therefore I have 1.4 (Since we're going to apply this figure to everything apparently) smiths to your one and it would make just as much sense as what you're saying.