1897 and 1912. Think about that for a moment.
My 16th birthday present was a Winchester Model of 1912. Made about 1922. And that gun was 50 years old when I got it. Still have it, too! Works just as well today as it did then, maybe even a tad better.
Yep, its all steel and wood. No alloys, no plastics. Besides the aesthetics of that, the design is superlative. You cannot wear one out in a human lifetime, and probably not in several. The gun has the capability to be readjusted for wear to a tremendous degree. Something not possible in other designs.
Not as slick working as an 870 (only a single action bar), but tremendously rugged, and dependable. I would expect the 870 to have some features that are improved over the Model 12, as it was designed nearly 40 years later.
Model 12s got their reputation from working, and working well under all, including the most adverse conditions. And they got it before most newer designs came on the market.
Complicated to detail strip? SO WHAT! They were not designed as "combat" shotguns, but as sporting arms. Faulting the design for that is like complaining that your Camaro isn't a pickup truck! Not applicable, unless you are being ridiculously unfair.
Never cared much for the 97, myself. Its drawbacks are the hammer, and bolt, biting your hand unless you have it out of the way. This was fixed in the Model 12. Also the ejector in the 97 is a little less robust, fortunately, it is easily replaced.
It is a tribute to these designs that they function so well as a combat shotgun, something for which they were never designed, not a shortcoming because newer designed guns function a little better in that role.
And many later designs are no where near as good, from a ruggedness and reliability standpoint. In the 1970s I was a military small arms repairman, and I can tell you from personal experience that the Win 1200 is not nearly as good a gun as the Model 12 for hard use. Rem 870s in those days were very good as well. Today? Not quite so much, I think.
The 97 got popular again, only becuse of the fact it is basically the only pump allowed in CAS shooting. Lots of old 97s stopped gathering dust in the back of the closet, and demand raised their price (and value) to the point where chinese copies are being made and sold in job lots. Its a good gun, but not as good as the Model 12, except where game rules give it the edge.
Any good modern shotgun will function as well as a Model 12, even be a bit slicker to work the action. But a model 12 will still be doing it for your great grandchildren, unless neglected or abused, and maybe even then. Not many newer guns will be able to do that, even with the benefits of modern design materials and manufacturing methods.
And yes, most model 12s do (like thge 97) lack a disconnector. Hold the trigger back and close the action and it goes off! A feature one must be aware of! Not a flaw, just a design feature from an age when the shooter was expected to be smarter than the gun!
Also not proper to bash the gun because it wasn't made for steel shot. Changes to US game laws made well more than half a century after the gun began production are hardly a fault of the design!
All else being equal (and it almost never is) bigger bullets tend to work better.