Eh, bronze weapons were in Radiant Dawn as well and they weren't that bad there (actually the -10 to enemy critical hit chance/skill use is a nice buff). I could see carrying one around to deal with bosses or something similar just to prevent those oh so annoying OHKO crits and skill triggers that force mission restarts. More of a situational thing than an everyday weapon.
I could also see uses for the other types as well. Stick a steel weapon on a heavy unit and it's basically just free damage, since their chance of a dodge or attacking twice is pretty low anyways. (Alternatively stick it on a very fast unit, since a -5 penalty to evasion isn't that much for them and they can absorb a -3 penalty to their speed for a dual attack with no problem). Similarly a silver sword could easily be something you stick on a finisher character, that bonus damage could be really nice and most swordsmaster-esque units are fast enough that their enemies don't have that good of a chance of criting them before hand. (And who attacks every single turn with a character like that anyways?
) Similarly a brave weapon could be great on an archer, since most times they shouldn't be being counterattacked anyways, or on a very heavy damage dealer who you rely on just killing the enemy in their two hits before they ever get hit back in return.
Sure, I'd probably stick iron on the majority of characters, but there are definitely some nice strategic usages for the other weapon types (all the knights+paladins with steel, archer's with brave weapons, a myrmidon or two with a silver weapon, one guy with bronze to deal with the boss, and everyone else with iron). Honestly I'm waiting to see if they are going to change the damage strength of some of the higher class weapons (silver, etc.) as well to make up for the fact that they never break now, which used to be one of their major balancing factors.