The thing about balancing artifacts (or whatever you want to call magical equipment) is that they should be balanced with the other ‘non-intrinsic’ character resources that a character can develop over the course of play. And should have as much investment required and limitations imposed as those resources as well.
Looking at it solely from the idea of Background dots (though actually you would balance them based on time invested x resources required), a four dot Artifact should have the same level of utility as a four dot Army or a four dot Spy Network or a four dot Shipping Company or a four dot Cult. It should definitely let you be better at doing things, much like having a cadre of trained spies makes you better at ferreting out the movements of the Wyld Hunt or a four dot Shipping Company helps you undercut the local Fair Folk slave trade and so on. But it should also require just about as much time to acquire as building that spy network or company, have restrictions on how you can apply it on the same scale and require roughly the same level of resources to deploy consistently.
Imagine the amount of money it takes to train, equip, deploy, march and field an army of 1000 soldiers to take on a rival kingdom. An artifact weapon that was as useful in taking on a rival kingdom should take that much effort to find/build, repair/maintain and expend about as much resources. Though the types of resources may differ. Armies need conscripts, arms and armor, food, medical supplies, training time and so on. A sword that creates volcano blasts capable of taking down that army would require various exotic materials, reagents, crafting and training time to use.
This is basically how you should be using demesnes and manses in your games. The idea of magic baubles is way too D&D, but securing a network of magical fuel depots and mines for more vespene gas magical reagents, or carefully managed bordermarch zones, or trade with demon soldaties, or bargains with local corrupt spirits… yeah, you can totally have magic bling. Ironically the way to preserve it is to both make artifacts more and less powerful at the same time; less Sword of +2 versus Dragonblooded and more tactical warheads.