Technology is already there, it doesn't need to develope up from nothing. If the Romans landed in Dom3 World, they wouldn't find themselves surrounded by primitive cavemen unless they happened to have Cave Men neighbors
but that's not what we're talking about. I'm not saying that because a nation has a Forge they'll suddenly leap ahead in the technological arms-race, I'm saying the Forge will give them more avenues and more choices. They can devote more resources towards specialization, not technological wonder-making, just specialization, something most if not all successful nations have done, usually within single generations, and often within just a few years. Something that also often enough LEADS to innovation, but, it's much more matters of fashion, hunch, elitism, taste, community, family and fad, than it is a matter of genius.
Look at the American Revolutionary War for example (hint-there are better examples): Everyone more or less had access to pretty much the same technology, there weren't the huge innovations brought on by the conditions of the Civil War, but basically it was English against English, with some addition of mercenaries and foreign soldiers of fortune etc, but basically everybody spoke the same language and prayed to the same god. Yet you'll find there was an ENORMOUS variety to the troops both sides deployed. You had everything from Indian skirmishers to White Indian-fighters to German Hessian knights to Kentucky longriflemen, and plenty of variety within the rank-and-file of the English and American infantries/calvalries. It's logical and it happens that nations develope different units for different purposes, and it seems to be the nature of war that fighters come in endless variety. Look at modern weapons-at it's most basic, a gunpowder weapon is a bullet, a barrel, a trigger, and the internal and external mechanisms which work together to propel that bullet to, into, and possibly through a target. A gun is superior to any weapon which has come before it to the point where an army armed with pretty much any kind of decent modern gun will defeat any army armed with more primitive weapons, providing the more primitively armed army doesn't have huge advantages over the one with the guns, and yet look at the incredible variety of guns. Yes, we modern folk can produce our ideas more quickly than people could in the past, but the answer isn't technology by itself, it's the reality of war and the reality of human response to warfare and strategy. The Forge represents a nation's ability to put the kinds of strategy that we call "mixed arms" "diversity of arms" and "arms-logistics" into effect in the game. It also represents a nation's internal diversity and a truer model of what the "unit" and the "fighter" really were.