The dreadnaught projects an arcane wrecking ball or sledgehammer that deals Force damage- emphasis mine. This reads that the weapon the dreadnaught uses is an energy construct, not a physical item.
Guardian? "You can discharge concussive blasts with strikes from your armor. The pulse counts as a Simple Melee weapon..." Your simple weapon isn't even your armor. Its an energy blast.
Infiltrators have a gemstone that shoots bolts of lightning. Despite the rules treating it as a simple weapon, its actually closer to a magic wand than a physical weapon you can enchant with magic.
I suppose that I should have compared the Armorer to the Rogue Soul Knife instead. Everything in the new Armorer is an energy construct or blast of some kind. They are not physical items that you can enchant. I think its pretty clear that there's nothing you can, or are supposed to, replicate, because you can't really replicate pure energy. The intent seems pretty straight forwards to me; these can't be magical items, because they're not physical items in the first place.
And, upon further investigation, I think I was wrong about the Magic Weapon applicability here too. I forgot that the spell doesn't work on magic items, and since you create the armor with a Magic Action, this counts.