Howdy
I suspect that in 1899 when the first 38 Military and Police came out there may have been those who bemoaned the lowering of quality from what had come previously. That is human nature.
Your criterion of including short throw actions probably makes your statement true. I don't remember exactly when short throw actions first showed up, I think it was shortly after WWII.
But I have lots of 'modern' Smiths from before 1947 and I think they do not take a back seat to anything later, with the possible exception of short throw actions.
I just took a look in the SCSW and it appears modern Micro Click rear sights and short actions first appeared with the K-22 Masterpiece (Pre War), only made from 1940 to 1941. Although this short action hammer did not resemble the modern one with the deep gullet between the hammer spur and the hammer body and the deep checkering on the hammer spur that we have come to associate with the modern short throw hammer. Like the one on your 1956 357 Magnum.
Also, a lot of folks deride the Bangor Punta guns, but the first Smith I ever bought was my Model 17-3 which I bought new in 1975. The quality of that revolver, both inside and out, is second to none.
The CNC machining inside the frame is second to none.
This Model 14-3 from 1974 is no slouch either.
So all in all, your premise is pretty subjective. But if part of your criteria is modern Micro Click rear sights and modern short throw hammers, I would at least extend the time period to some of the Bangor Punta guns.