With a modern, STEEL, barrel wearing the muzzle will probably required thousands of rubbings. But, the reason we use SS rods over Brass, or wood, or synthetics, is because the softer materials can hold microscopic residue, including silicates. These can be abrasives even on a steel barrel. The wear is going to first appear on the Lands, and only later in the grooves, at the muzzle. But, when the lands are worn, they let gas blow by and cut your patch, and even the lead ball itself, reducing accuracy. The softer the material the rod is made from, the easier it is to pick up GRIT, and turn it into an abrasive.
The habit of using a muzzle protector dates back more than 120 years when Post Civil War Target matches with MLers were still held, but the barrels were still being made of softer IRON- not Steel. Even the few steel barrels made back then were softer, and not made of the alloys we have today. The industry did not yet know how to make the alloys or control the mix of metals that made up the alloys. Most of those problems were not solved by the industry until after WWII, and grew out of the Auto industry, not the gun industry.
Coning a barrel is for the purpose of centering and easing a PRB down into the barrel, with the least distortion, and limits the possible tearing of a fabric patch, or to a Paper Patched bullet. Its not to protect the muzzle from poor handling techniques during cleaning and loading.
As for choosing one metal Range rod over another, that is really a personal choice. I happen to like my Stainless Steel rod, but I also have a hickory rod I made for my DB 12 ga. and an Aircraft aluminum alloy rod for my 20 ga. fowler. A Range Rod is a tool. Nothing more. Buy the best tool you can afford, and you will have no regrets. I personally don't have a lot of faith in either brass rods, or brass tubing for this kind of tool. But I know others who swear by them, and wouldn't have anything else. Its your choice.
A worn muzzle is always worn unevenly- mostly because of the habit of resting the barrel itself against a bench or table, so that the same flat of the barrel faces the handler. He strokes the rod in and out of the barrel with the same hand, time after time, wearing the same side. By contrast a coned barrel is done so with a cutter, or controlled abrasive rod, so that the coning, or bevel is even all around the mouth of the barrel. The lands are reduced by the coning to groove diameter for enough distance behind the muzzle, to allow a PRB to be seated with only thumb pressure in the barrel, and the fabric trimmed off at the muzzle with a patch knife. The bevel of the cone is long enough that when a ramrod is pushed against the PRB, it slowly Grabs the patch on the lands, until the Patch and ball are starting down the full diameter of the bore to the bottom of the barrel, where it can be seated on top of the powder charge..... You did remember to pour powder down the barrel FIRST, before you began pushing that PRB down it???
:thumbsup