Tip: Template for reducing late game MM hell

[Illuminated One]

Well, at least one thing is quite sure that banning hammers will negatively affect earth nations (Ulm, Marverni, Yomi, Agartha, Vanheim, Machaka, Atlantis, out of Memory there is only Hinnom where a nerf would be good).

Maybe it would be better to just note down exactly where the most time is spent.
Taking the dwarven hammers if I understand it correctly the reason why you are considering them MM nightmare is that you have to collect them from 300 mages in 100 provinces?
That's a fact, but if you blame that on the hammers that's only a perspective.
Why not blame it on having to have 300 mages or a too large map?
I mean seriously, you have zero problems with managing your dwarven hammers if you set up a couple of forging provinces into which all your dedicated forgers go (and they are not used for generally spamming mages). The only problem is that the gold could have been spent on additional research centers and you loose some research turns moving around. And this is - I repeat myself I know - the really broken mechanic imo. Virtually every strategy game encourages you to organize your empire (like building cities in sensible locations or choosing the right amount of research and industry centers) while dominions punishes you for it.