While I would think the Steel Wool wrapped brass brush would be actually "Needed" only in severe cases I also think the wool is of a very soft grade of steel & one would likely wear out two or three Drill Motors without removing any significant amount of metal from the gun's bore.
I think you are probably right in that, but there is also the considerable risk of little bits separating from the steel wool and getting in 'the works', under the ejectors, on the joint hook and other undesirable places. Its just something I wouldn't want in my guns!
There are steel brushes (called 'Turks head' brushes) that can be used for the removal of rusting, corrosion and I suppose very severe fouling. They are very severe in action and although I have a old one, I have never used it