Harder alloys are 'stronger' but being harder to start with assures they will also crack and split sooner. Fed uses a slightly softer alloy that is plenty strong enough for normal pressures and will last much longer than harder alloys if the pressures are held down a tad but it doesn't lend itself to hot-rodding as well as others.
It is my understanding that all brass cartridge cases are made from the same alloy, C2600 A.K.A., "cartridge brass". If that be true, the "hardness" of the brass used by different manufacturers would be of the same hardness. The only way brass can be hardened is by "working" (plastic deformation), the brass. The only way brass can be softened is by heating it . The "working" and serendipitous "hardening" is caused by the drawing or swaging process. After the case is formed, manufactures will heat-treat (to soften), the mouth shoulder of the case. The discoloration is usually polished off by the manufacturer before shipping with the exception of some relatively heavy "African" cartridges where that has become a tradition.