Some excellent observations. To begin with, the machinery wasn't "less Precise" it (machinery) just operated differently. The original sample examples you speak of were made to very close tolerances and functioned, for the most part, flawlessly. For the time period, the materials were not actually structurally inferior. The nature of the "Iron" used to build percussion guns was quite solid and more than sufficiently sound.
We speak and advise of the "need" for some extensive "work" to make modern replicants acceptable for CAS play. The reason for this, we ask and expect the modern replicants to perform to a level never thought of in the 1860s or 70s. Guns of the era were not expected nor asked to fun for more than 6 rounds at a stretch. Not 6 to 12 stages of shooting..... then we must look to the ammunition and the ignition system.
By ammunition, I speak primarily about the Caps. Period caps were heavier, tighter, and waterproof. The guns had a massive spring to assure ignition. The caps stayed on the nipples and "cap sucking" (term coined by Mike Belliviue) therefore, was not a problem. In fact, Colt and his salesmen use to put a loaded gun in water during their presentation. Then pull it out and it fired just fine. Modern Caps, not so much. The heavy springs also promoted accelerated wear of the lock works and frames.
To run these replicants "fast" we reduce the springs, Set the timing to a gnats patute, smooth the interior of the frame to support light springs, recut forcing cones, and some of us (Me) chop, channel and french the headlights.
Fixing the Arbor you speak of, is only currently required for Uberti built replicas. Colt never had this problem of a miss-fit between Arbor and Barrel. ALL but a few Uberti have a ludicrous fit problem between the Barrel Lug and the Arbor. For a Uberti to run like it is suppose to, the VERY FIRST thing coming out of the box is to fix this deficiency.
It is unfortunate that you have been exposed to sample examples of the Originals that have been used primarily as childs toys, viewed by the owners as junk and abused to the point they are junk. Original Percussion guns that have had proper care usually function as well today as they did 150+ years ago. Others, unfortunately, have become rusted junque.
Maintain the correct perspective. Percussion guns were not "reloaded" in the heat of hostile action. Fighting men ran one dry, discarded it and went back to work with another already loaded pistol. The Original guns fouled out just as quickly as ours, we, on the other hand, reload. I suggested once, to a "thread counter" we play "exactly" as was done in those halcyon days of yesteryear. You want to shoot a 6 stage match as "they" should have?? Really?? OK, bring 12 fully loaded pistols to the match (remembering, YOU still have to clean em).