The bonus from forge is a "Base Bonus" to each defense stat, and doesn't affect armour, so it only gains the bonus from the forges that was in the city, from which the unit was created.

In the current system you have to separate the idea that the forge have anything to do with the crafted weapons or armour, and just think its a static +x to defense, like having the +3 defense trait, but for free.

Hope this clarifies

Sincerely
~ Kongdej

I think that is part of the strategy. Do you want to pump out the units early or try to hold off until you have built some better buildings in your fortress. I usually try to mix it up a bit. Lot of times those earlier units get taken down hard by some early big bad monsters nearby, so no major loss.

Nice way of wording that and I agree.