I think that bronze being better than iron is strictly correct, but modelling that does get you into kind of an odd corner since iron did in fact displace bronze. (Though part of that is said to be just the relative availability of iron versus tin + copper, which oddly enough my current map models really well. I just now found tin, and only one big vein of it so far.)
People were making steel of some kind by accident before they ever knew what they were doing, since carbon isn't exactly some rare element that wouldn't be found floating around a forge. More interesting to me, the first people to make steel deliberately and reliably still didn't know exactly why it all worked. Europeans went through a period where they thought steel was the purified form of iron, which is obviously counter-productive when you want to be adding things in. So the succesful steel-smiths of the time were those who had idiosyncracies or superstitions that lead to them putting in enough carbon to have some left by the time they'd "purified" it. And the Japanese stalled out even earlier; the multi-folding technique for katanas, while justly famous, partially just compensated for their crappy steel metallurgy.
So... again conceding that bronze > iron, 2010 seems to model only regular iron, with a straight jump to nearly modern steel, and no allowance for accidental steel or folded/damascene steel. It'd be nice if masterwork iron weapons "graded up" closer to steel, to represent that.
Or I just need to adjust my view of what's happening in the game. Maybe the dwarfs *don't* know exactly what they're doing or why when they grab flux for pig iron, and the inventory management end of flux, pig iron and coke is just a convenience for me.