Well, I've said this before but, the inner workings of the Models 27 & 28, are no heavier duty than the K frame models, but the cylinder is more robust, as is the frame. The L-Frame proved it unnecessarily so.
As far as the Model 19 "falling away", I certainly don't remember that, as it was actually one of the most "sought after" pistols for L.E. in the 60s and 70s before the auto craze hit L.E.
I was part of tha era here in North Central Texas, and many a State Trooper was envious of our lighter, more carry friendly, Model 19s, and 66s, than their Heavier 28s, and the occasional "long action pull" Pythons.
No the Model 19 didn't like a steady "high volume" diet of full house 357s but, only in TRAINING would this have occurred. In training scenarios, the Model 19 actually held up better, as the rapid firing of "the light training loads" used in those days, battered both the cylinder hand, and the cylinder stop of the excessively heavy Model 28 cylinder.
Now! I'm not bashing the Model 28. I used one to end a disagreement in 1977. What I AM saying is, the BIGGEST difference in strength, is the CYLINDER. The frame is bigger, but the internals, not really. That's pretty much it.
Like it or not, believe it or not, as Elmer Kieth used to say: "Hell I was there." As a sworn officer, and state certified police firearms instructor. When the 357 magnum, was still king in Texas L.E.
By the way. On an historical note. Bill Jordan collaborated with S&W on the Model 19, WHY? Because police officers were complaining about the unnecessary weight of the N-Frame revolvers in day to day carry.