Steel cases ARE NOT harder than brass. Plenty of info and tests online that prove that both are about the same and in some cases the brass is harder. All it takes is 5 min of Google search.
Since steel is cheaper than brass and just as soft (or softer according to your supposed Google searches), why don't all loaders use it instead of brass? Why doesn't our military use it? Why doesn't Hornady load Steel Cased 9mm? Why do even former Soviet republics make brass cased pistol ammo instead of steel cased? Why does brass cased ammo outsell brass or aluminum worldwide by margins of 10+/1?
Having worked for a bullet manufacturer/ammunition loader for over 5 years, I can with authority say your statement is false.
The only advantage steel has over brass is it's cheaper. It's not equivalent in other performance elements. It IS harder. It does not contract in a chamber after firing as well or quickly compared to brass. It is usually harder to extract. Russian QC is usually substandard compared to US manufacturers, and powders are dirtier. Bi-metal bullets are very hard on throats and barrels (not so much in pistol bullets). Military style primers used in Russian ammo are often very hard. Steel rusts unless it is either lacquer coated (Wolf ****) or zinc plated. Lacquer coating fouls tight chambers. Russian caliber chambers are designed for and cut large for easy extraction of their cheap steel cased ammo. Brass runs fine in them because it is so malleable. The reverse is not always true about steel in SAAMI spec chambers.
Tula seems to be the best of foreign steel ammo.
Does it work? Yep. Should you use it? Yep, if cheap is important to you. But not because it is the same as brass cased ammo, because it ain't.