Better steel than maybe the mid 1800's. Better steel than modern Ruger, Colt, or S&W? Very doubtful. The cylinders on my Pietta revolvers are very soft. The 1858 frame is very soft as well. Mine are from the late '90s and early 2000's so I guess that is like the worst ones to have. I don't own Uberti pistols but my dad had a couple and they had issues as well. Not sure when they were manufactured. My point is that I like them but they are far from fine weapons. If they were they would be over $1000.
I have my Pietta 1858 shooting pretty good but the cylinder bore isn't in alignment with the barrel bore. Planning on picking up a 36 cal cylinder and line boring it into alignment. My 1860 is better in alignment and the frame seams to be made out of way better steel. The bad on that is the timing is awful. Still working that out. And it had the arbor issue.
I would wager that the originals were better. Yeah they weren't for sure what the steel was as they were lacking the metal analysis tools we have today. That being said they indeed had some pretty decent steel. They had been making steel for how long by the 1860's? Like 350 years? lol