There are so many responses I can't read them all and see what others have to say but will offer my 2 cents worth. You missed the IND R1-9 in your thoughts which to me was one dandy, durable piece of equipment.They were old technology when new but they did the job and moved, fast.Averaged some 40 years of service. The deferred maintenance of later years caught up with them and they became rather sick but held out while they were needed.
You mentioned the pre-unification IRT cars. They were built when their respective technologies were still almost in infancy; the old High-V, Low-V, Flivver and Steinway cars with the exception of the last ones built served the system an average of about 45 years, sometimes more. They survived the bankruptcy of the Interborough, World War II with I'm sure much of the skilled shop help away at war, and until their end between l955 and l964 were still maintaining the schedules they were built to maintain which were within some 10% margin of what the replacements were capable of.I know many people disagree but I loved them and appreciated what they represented and admired them for how well they were made and all the years they did a great job.
Everything has its time , we're thinking of l904-1925 equipment. Things move on and I've accepted that what was dear to me couldn't be forever and becomes obsolete. But that old stuff was great [for its time] and didn't owe anyone an apology.