It depends on what version you are playing too.
If you are playing on the "old" one, then you can reach steel grade things out of steel wood, that can be grown in farms (needs a full year to grow).
For armours, refining leather to the highest grade, can get you materials that are very good, to use as under armour layer, and refining chitin and shells can also get you really good armours.
It is also possible to make arrows/bullets/bolts out of steel wood, for steel grade ammo.
Of course, a metal smith is always good to have, because masterwork quality weapons and armours are extremely potent, and some of the highest value stuff for your nobles are also made out of metals (like gold or silver).
But truthfully, you don't actually require a metal smith, as it is completely feasible to survive by making good use of other things, like ranged units, traps, poisons...