From a gunsmith's perspective
Roll pins. Used to be solid pins. Used to be screws before that. Used to be screws that were secured by a lock screw (think the old Mauser 98k or some of those earlier Colt DA revolvers).
MIM. OK, it works when used properly. But it used to be casted or forged. Casting is cheaper (cost wise) and forging was very labor intensive (not just forging but a lot of grinding/filing to make it fit).
Castings v. forgings. Casting is the old new back in the '60s when Springfield Armory was first trying it out to test its feasibility. They got shut down before it could be implemented on a wide scale measure. Castings must be thicker for equal strength. However, it's just as viable for fabrication as forging and is cheaper and more flexible (for the designer). I wouldn't hesitate to buy a Ruger.
Polymers. OK, some advantage like weight and no rust. But it used to be steel.
Plastic (hardware). Used to be wood, but wood swells, warps, puts pressure on the metal parts that affects the harmonics. Even if it is a safe queen, the stains can darken with age, hiding the wood's beauty. Conclusion: Wood for beauty is unrivaled, but plastics is for rough field use.
One area that hasn't affected quality is cold hammer forged barrels. For the speed that they produce a barrel and cost, they are excellent.
Finishes. The old finishes like hot rust blue and nickel plating don't hold a candle to Cerakote and Duracoat for durability. Express blue is one of the prettiest though for classic rifles. So, this is a yes and no response. Hot rust blue and express blue for pretty guns. Spray 'n bake for field guns.
Ultimately, what does the customer want and what can you provide for your customer? Consider that the smith must make a profit if (s)he is to remain solvent.