I am not sure what the definition of “older firearms” would be, but for the sake of this post I would limit it to post-WW 2 through sometime in the 1960’s (and NO, I can’t substantiate that end date), and because pre-WW2 manufactured firearms did not have the benefit of materials and techniques developed during WW2. With some few exceptions in what I call the “higher end- more expensive category”, I believe that the firearms we find today have sacrificed artistry and pride of craftsmanship for functionality, and in many cases, name brand manufacturers favor short term sales volume and cost reductions at the expense of longer term brand reputation. However, it would be fair to argue that carbon fiber stocks and stainless and more modern steels are an improvement with regard to the materials durability.
If you look at the fit and finish of “off the shelf” older respected name brands of firearms as compared to what we have today you will not find the same product pride, quality of workmanship, and what I call “artistry” that was found on older firearms; for example: look at the standard bluing & fit of a regular S&W Model 1955 revolver or a Winchester Model 63 .22 rifle...these weren’t custom or extraordinary offerings; they exhibited the standard quality that we expected. Ever work the action of a pre-64 Winchester Model 70 for 3 rapid shots?...if you did then you know the meaning of smooth, reliable functionality for a mass produced rifle.
For modern firearms carbon fiber stocks (sometimes frames on handguns), aluminum frames, barrel inserts, and even plastic parts have reduced the weight and cost of manufacture for firearms and with the exception of plastic parts added durability. Many military firearms have benefited from new manufacturing techniques and materials which, IMO, is an improvement, however, this has carried over to the civilian market which I view as a mixed blessing. Go on over to the S&W Forum, and look at the complaints about the workmanship for their products post 1980 (or 1970, I forget the exact date); HD- Ghost states that he would not buy a Colt made since 1970 (I can only speculate that is because of poor quality control?). Law suits force manufacturers to add unnecessary “safety features” to their products some which actually inhibit quality functioning of the firearm (I’m getting ready for opposing comments on that statement). I personally love the fit & finish, craftsmanship, “feel”, and the quality of the older guns.
Durability is not an issue with me, because my father was a stickler for firearm maintenance and care which I have embraced for older OR modern firearms. “Modern” firearms have the potential to greatly benefit from new materials and manufacturing techniques, BUT the manufacturers will have to revise their standards to improve their quality control, pride of craftsmanship, and pay more attention their longer term survival; although there were some other causes the same issues named above plagued Remington Arms…and look what happened to them. All said and done, whatever your preference, I believe that many older firearms fall (very loosely) in the category of massed produced “works of art”, and, sadly, that era has long passed.