By all measures, the quality of vintage blades were better. I'm talking about stainless blades from the 60's through the 70's or so. No doubt they can make them better today, but to just make them as good would put them out of reach of practically their entire market base. We, guys who wet shave as a sort of hobby, are a small fraction of men who shave with DE razors.I am not sure if the quality was better. Yes, they need now produce cheaper blades, but the machinery and technology got much better. I have one Gillette blade from 1920something. It is not flat. It shows typical production defects of wrong roll milling. But hardened carbon steel is harder than stainless. So the material might be a reason for longer durability.
I have a reprint of a German catalog from 1912 from a store similar to Sears & Roebucks. It has lots of no-name copies of Gillette razor sets and even one closed comb razor. The price of a no-name blade is 0.20 Mark. In Germany we have official statistics of the average annual income since 1891. I think it is the best way to compare prices here in Germany. ( Durchschnittsentgelt – Wikipedia - https://de.wikipedia.org/wiki/Durchschnittsentgelt ) 0.2*(39000/1164) = 6.70 Euro = USD 7.40 per blade. So one blade in 1912 cost as much as 100 blades now.