First let me say I am not a Wrestling Fan & George Steele was not a name I recognized, sorry about that. I have therefore made no disparaging remarks as to your name.
I do however see a few Flies in the Ointment though concerning some of your statements. First powders from around the range of Unique & faster reach their peak pressure Closer to the breech than does Black. Secondly most doubles built from around the 1890's onward whether in steel Damascus or twist had their chamber walls thicker than some earlier guns with the knowledge they were apt to be used with smokeless. In shoe rt They were designed for smokeless & they stated so.
As to this deterioration from Galvanic Action this is quite possibly theoretically so, in Practice however it just doesn't appear to be occurring.
In Practice it is actually much easier to find accounts of failures in early steel barrels due to material flaws than for the welded barrels. A void in the billet when drawn into a tube would leave a seam, many were caught in proof or finishing, but not all. The forging process on the welded barrels eliminated these voids. There was of course always the possibility of slag being trapped, referred to as Grey's in the welded barrels. In reality these were more cosmetically unattractive than actually dangerous.These were not drawn put into seams but at worst were no more than the vent hole in a flintlock.
