I have a small example of older to "very old" S&W firearms. I have revolvers made in 1913, 1923, 1947, 1948, 1950, 1973, 1983, 2017, and 2019. All of the ones built from 1983 and prior are in perfect mechanical condition, and shoot well with factory ammo and factory equivalent handloads.
Only the 1947 and 2019 ones ever required any work, and as both are 22LR, needed chamber reaming to keep from being stubbornly dirty and hard to load and eject. A problem with S&W 22's for over a generation, it seems. Borrowed a reamer, and a few minutes work on each, they are slick and perfect.
The 2017, a 637, survived a double-charged Winchester Silvertip at a range, and had no ill effects other than a stuck case that was hard to pound out with a dowel and hammer. It works fine, as it did before. Hate the lock hole in it, though. Not an improvement.
All the rest are great shooters, and the two oldest are pre-and-post WWI pieces which are as tight and functional as brand new.
The 1973 and the 83's are all j-frames, and all in great condition. My 36 and 38 vie for the best double action of any of my Smiths, and my 1983 60 has great single action.
Were they built better in "the old days"? Maybe. The designs have changed little in over 100 years, now, just engineering and safety improvements. But the gunsmithing ability of the assemblers? Yes they were better in previous generations. More care and pride in the work.
Material, alloys, heat treating, and such are much better today.
Only my 637 says +P on it. All the other 38's are standard, and my 1923 44spl, factory ammo only, though factory loads have changed very little over the years. No Skeeter or Keith loads for it.
Just like everything else today, I think it's all about quality control.
It ain't as good as it used to be...