They never use it. They have all that they need; they are not driven by greed to keep growing. Really, most of their stuff won't ever be put to use.

And again, they're pretty damn old. With enough research, and with their skills, they could make a machine the drills or uses a laser to make a hole deep enough, and then a machine that sends mineral/ore-specific waves that would break up the selected ore/mineral type. Then using a heat-pulsing machine, with sufficient energy and advancement, both of which the Supremes have in abundance, and they could melt all this, and pull it up through the hole. Or just a very efficient machine.

You have 100 galaxies, and trillions upon trillions of people. They have thousands of galaxies, with only tens of billions of people in a single fleet.

Tell me, how is this super-efficient machine used very rarely by a very small-population group overpowered, when, even with every single known piece up and running on mineral-rich worlds, their max output in a week wouldn't even come close to the Equestrians' average output in a day.

Very efficient, but it's like 3 drills compared to 3000 miners with good, strong pickaxes.