This is somewhat of a loaded question. Personally while I own a few older firearms, if needing repair parts are not always available, parts that are available do not just drop in and require fitting by a talented gunsmith and in some cases parts need to be fabricated by even more talented gunsmiths.
Within the last year a close friend had the operating rod on a vintage 22 semi auto crack. Made of pot metal it could not be repaired and required the talents of a highly skilled gunsmith with a very well equipped machine shop. He manufactured a new part, made from high grade aircraft quality aluminum the new part fits and it works flawlessly.
Newer firearms, as one has pointed out are made on CNC equipment, for the most part untouched by human hands, I'm sure in some cases from Billet metal to the box. This is probably causing much of the angst among the complainers of the world about quality control. If a part breaks or wears out, which is not really all that uncommon the new part will usually drop right in without any fitting. The metals used in new firearms are of much higher quality providing that a real base metal is used and not a part made by injecting metal into a mold and thus subjected to any variety of issues due to differences in molds, temperatures and composition of the metals used not to mention differences in cooling rates which can affect metal hardness and durability.
In essence are older firearms made better than new ones? Yes and no. The materials used in older firearms are most likely not as durable as in newer firearms. but newer firearms do not get the attention to detail once lavished on every firearm. So from strictly my point of view, they are about the same, but for different reasons.